PO Number on Invoice UK — What It Is, Why It Matters & How to Get Paid by Public Sector Clients

You invoice an NHS trust for £2,400 + VAT for a graphic design project. Two weeks later, your invoice is returned unpaid with a note: "No valid purchase order number. Please resubmit with PO."

You check your invoice. You quoted your invoice number, the project description, the client's name, your VAT number, payment terms — everything looked complete. But you missed the purchase order number because the client never told you they needed one.

Now your invoice is invalid. The trust's finance system will not process it. You must cancel the original invoice, get the PO number, and reissue a corrected invoice. Payment is delayed by three weeks because of one missing reference.

This is the reality for thousands of UK freelancers who work with NHS trusts, local councils, universities, and large companies that operate "No PO, No Pay" policies. Without a valid purchase order number on your invoice, you do not get paid — even if the work is done and approved.

This guide explains what a PO number is and how it differs from your invoice number and a payment reference, covers No PO No Pay policies with links to real NHS trust and council guidance (NHS Property Services, Wirral Council, Renfrewshire Council, RNOH NHS Trust), shows you step-by-step how to get a PO before you start work with a copy-paste email template, explains exactly where and how to put the PO on your invoice, fixes the most common problems (invoice rejected for missing or wrong PO, PO value used up, PO expired, PO raised after the work, client's PO terms differ from yours), covers getting paid on time once the PO is on the invoice, includes a worked £ example with a freelance designer invoicing a council, provides a PO checklist with designed tick bullets and an FAQ, briefly mentions SoloPad's invoice notes feature (only if verified in the code), and finishes with a short summary and soft 30-day free trial CTA.

What a PO number is (and how it differs from your invoice number)

A PO number (short for purchase order number) is the client's internal reference for their approval to buy your services. When a client raises a purchase order, their finance or procurement team assigns it a unique number (the PO number) and records what they are buying, from whom, for how much, and by when.

Example PO numbers: PO-45892, ORDER-2026-0312, PO/2026/1042, GPC-20261015-01

The PO number appears on the purchase order document (a PDF or email the client sends you) and in the client's accounts system. When you invoice the client, you must quote the PO number on your invoice. The client's finance team (or their automated system) matches the PO number on your invoice to the PO in their system. If the numbers match and the invoice amount matches the PO value, payment is approved. If the PO number is missing or wrong, the invoice is rejected.

PO number vs invoice number vs payment reference: what is what

These are NOT the same. Here is what each means.

Your invoice number:

✓ Your unique identifier for the invoice you send
✓ Set by you (e.g. INV-2026-042)
✓ Required by HMRC for your records and VAT compliance
✓ Always on your invoice (top section, near the date)

For full guidance on invoice numbering, see invoice number UK.

PO number (purchase order number):

✓ The client's reference for their purchase approval
✓ Set by the client (e.g. PO-45892)
✓ You include it on your invoice if the client provides one
✓ Required by many clients (especially NHS trusts, councils, large companies) for payment processing

Payment reference:

✓ The reference the client puts in the bank transfer when they pay you
✓ Often (but not always) the same as your invoice number or their PO number
✓ You specify it on your invoice (e.g. "Please use invoice number INV-2026-042 as your payment reference")

For more on payment references, see remittance advice UK.

Who issues the PO?

The client (the buyer) raises the purchase order. You (the supplier) receive it.

The process works like this:

1. You send the client a quote or proposal for your services (e.g. £2,400 + VAT for a website build)
2. The client's finance or procurement team reviews your quote
3. If they approve it, they create a purchase order in their system
4. The PO records: your business name, the project description, the agreed amount (including VAT if applicable), the PO number, and any terms or conditions
5. The client sends you the PO (usually by email or via a supplier portal like Tradeshift, Coupa, or SAP Ariba)
6. You start work once you have the PO
7. When the work is complete, you invoice the client and quote the PO number on your invoice
8. The client's accounts team matches the invoice to the PO and processes payment

Key point: You do NOT create or control the PO. The client does. Your job is to ask for it before you start work and quote it correctly on your invoice.

"No PO, No Pay" policies — NHS trusts, councils, and large companies

Many UK public sector organisations and large private companies operate a "No PO, No Pay" policy. This means:

✗ No valid purchase order number on your invoice = invoice returned unpaid
✗ Wrong PO number = invoice rejected
✗ PO expired or value exceeded = invoice rejected

The policy is not optional. If the client tells you they operate No PO No Pay (or if you see it on their supplier guidance page), you MUST get a PO before you start work. Otherwise you risk doing the work and not being paid for weeks while you fix the invoice.

Real examples: NHS trusts and councils

Here are real No PO No Pay policies from UK public sector organisations. These are live pages as of October 2026.

1. NHS Property Services

URL: https://www.property.nhs.uk/how-we-work-with-you/partners/suppliers/

What they say:

"Wait for a valid purchase order before supplying goods or services. Invoices submitted without a valid purchase order will be returned. Supplying goods or services before receiving a purchase order is at your own risk. All purchase orders and invoices must be processed through Tradeshift."

What this means for you:

• Do not start work until the PO arrives
• All invoices go through Tradeshift (the supplier portal)
• No PO = invoice returned

2. Wirral Council

URL: https://www.wirral.gov.uk/business/tenders-and-contracts/no-purchase-order-no-pay-guidance

What they say:

"Since 1 April 2019, Wirral Council has operated a No Purchase Order, No Pay policy. Invoices without a valid purchase order will not be paid. If you submit an invoice without a valid PO, you will need to send a replacement invoice quoting the correct purchase order number."

What this means for you:

• Policy in force since April 2019
• Missing PO = not paid (not just delayed — NOT paid)
• You must resubmit with the correct PO to get paid

3. Renfrewshire Council

URL: https://www.renfrewshire.gov.uk/business-and-licensing/business/suppliers-contracts-tenders-and-invoices/how-we-pay-suppliers-goods-works-and-services

What they say:

"Purchase orders are raised for all goods, works, and services. Goods receipt or service validation is required before payment can be made. We pay valid invoices within 30 days of receipt."

What this means for you:

• PO required for all work
• Payment only released after goods receipt / service validation (confirmation that you delivered what the PO specified)
• 30-day payment term starts from receipt of a VALID invoice (one with a matching PO)

4. RNOH NHS Trust

URL: https://www.rnoh.nhs.uk/news/rnoh-introduces-no-po-no-payment-policy-1-april-2025

What they say:

"From 1 April 2025, the Royal National Orthopaedic Hospital NHS Trust will operate a No PO, No Payment policy. This is in line with most other NHS Trusts."

What this means for you:

• NHS trusts are adopting No PO No Pay as standard practice
• If you work with any NHS trust, assume a PO is required unless told otherwise

Large private companies

It is not just the public sector. Many large UK companies (especially those with 500+ employees, global corporate parents, or SAP/Oracle finance systems) also require POs. Examples include:

• Consultancies and professional services firms
• Retailers and logistics companies
• Technology and software companies
• Construction and engineering firms
• Media and publishing companies

Rule of thumb: If the client is a large organisation with a procurement or finance team (not a sole trader or small studio), always ask "Do you need a purchase order for this work?" before you start.

Step-by-step: how to get a PO before you start work

The safest way to avoid invoice problems is to get the PO before you do the work. Here is how.

Step 1: Ask if a PO is required (before you quote or accept the job)

When a new client contacts you (or when you pitch for work), ask early:

✓ "Will this project need a purchase order?"
✓ "Do you operate a No PO No Pay policy?"
✓ "If a PO is required, who raises it and when will I receive it?"

When to assume a PO is required:

• NHS trusts, hospitals, and healthcare organisations
• Local councils and public bodies
• Universities and schools
• Large companies (500+ employees)
• Any client that mentions procurement, supplier portals, or purchase approval in their emails

Step 2: Confirm PO details before you start work

Once the client confirms a PO is required, ask:

✓ Who raises the PO? (Usually the finance team or procurement)
✓ What is the PO number? (Ask them to send you the PO document or email you the PO number)
✓ What is the PO value? (Check it matches your quote, including VAT if applicable)
✓ What is the PO end date or expiry date? (Some POs are valid only until a certain date or financial year-end)
✓ Does the PO cover all phases or just the first invoice? (For phased projects or retainers, clarify whether you need one PO or multiple)

Example email:

Subject: PO required before we begin — [Project name]

Hi [Client name],

Thanks for confirming you would like to proceed with [project description] at £[amount] + VAT.

Before I start work, please can you provide the purchase order number? I understand your organisation operates a No PO No Pay policy, so I want to make sure I have the correct PO to quote on my invoice.

Please confirm:

✓ The PO number  
✓ The PO value (should be £[amount] + VAT = £[total])  
✓ Any expiry or end date on the PO  

Once I have the PO, I will begin work and keep you updated on progress.

Thanks,  
[Your name]

Copy and adapt this email. Polite, professional, protects you.

Step 3: Check the PO document when it arrives

When the client sends you the PO (PDF, email, or supplier portal notification), check it line by line:

✓ Your business name is correct — Matches your invoice name (your trading name or limited company name)
✓ PO description matches your quote — The work described on the PO matches what you agreed to do
✓ PO value matches your quote — Net amount, VAT, and gross total are correct
✓ VAT treatment is correct — If you are VAT registered, the PO should include VAT at 20% (or the correct rate for your service). If you are not VAT registered, the PO should not include VAT.
✓ Payment terms are stated — E.g. "Payment within 30 days of valid invoice"
✓ PO number is clear — You can read it and will quote it exactly on your invoice
✓ Expiry date (if any) — Note the date. If the PO expires before you finish the work, ask the client to extend it or issue a new PO.

If anything is wrong, query it immediately. Do not start work until the PO is correct.

Example query email:

Subject: Query on PO [PO number] — VAT amount

Hi [Client name],

Thanks for the purchase order (PO-45892).

I notice the PO shows £2,400 + £0 VAT. However, I am VAT registered (VAT number GB 987 6543 21), so the correct VAT is £2,400 × 20% = £480.

The total should be £2,880 (£2,400 + £480 VAT).

Could you amend the PO to include VAT, or let me know if there is a reason the PO does not include VAT?

I am ready to start once the PO is correct.

Thanks,  
[Your name]

Step 4: Do not start work without a valid PO

If the client says "We will raise the PO next week, but can you start now?" — say no.

Why:

• NHS trusts, councils, and large companies state clearly: supplying without a PO is at your own risk
• If the PO is delayed or never raised, you have no proof that the client approved the work
• You may do the work and then have no PO to quote on your invoice, which means no payment

Polite reply:

Hi [Client name],

I understand you are working on raising the PO. Unfortunately, my terms require a valid purchase order before I begin work, in line with your organisation's own No PO No Pay policy.

Once the PO is raised and you send me the PO number, I will start immediately.

Thanks for understanding.

[Your name]

Exception: If you have a long-standing relationship with the client and you trust them to raise the PO within 48 hours, you can start at your own risk. But get the PO number in writing as soon as it is raised.

Where and how to put the PO number on your invoice

Once you have the PO and the work is complete, you invoice the client. Here is where and how to quote the PO number.

Where: Invoice header section

Put the PO number in the header of your invoice, near your invoice number and invoice date.

Good placement:

Invoice Number: INV-2026-042  
Invoice Date: 15 October 2026  
Your PO Number: PO-45892  
Due Date: 29 October 2026 (Net 14)

Or:

Invoice: INV-2026-042  
Date: 15 October 2026  
Purchase Order: PO-45892  
Payment Terms: Net 14 days

Bad placement:

✗ Buried in the footer or notes section (the accounts team may miss it)
✗ In the middle of the line items (confusing)
✗ Not labelled (just writing "PO-45892" without a label)

Label it clearly:

• "Your PO Number:"
• "Purchase Order:"
• "PO Ref:"
• "Client PO:"

Some clients specify the exact label to use. Follow their instructions.

How: Exact match, no variations

Quote the PO number exactly as it appears on the PO document.

✓ If the PO says PO-45892, write PO-45892 on your invoice
✓ If the PO says ORDER-2026-0312, write ORDER-2026-0312
✓ If the PO says GPC/2026/1042, write GPC/2026/1042

Do NOT:

✗ Abbreviate or shorten it
✗ Change the format (e.g. writing "PO 45892" when the PO says "PO-45892")
✗ Add extra zeros or letters
✗ Guess if you are not sure — ask the client to confirm the exact format

Automated invoice-matching systems are strict. One wrong character and your invoice will be rejected.

One PO per invoice (unless told otherwise)

Default rule: Use one PO per invoice.

Example:

• PO-45892 for Invoice INV-2026-042 (£2,400 + VAT)
• PO-45893 for Invoice INV-2026-043 (£1,800 + VAT)

Exception: If the client tells you to use the same PO for multiple invoices (e.g. a retainer PO that covers three months), follow their instruction. But clarify:

• How many invoices can you raise against the PO?
• What is the total PO value?
• Do you need to split the PO value across invoices, or can you invoice as work is completed?

Never split one invoice across multiple POs unless the client specifically asks you to.

Line items should mirror the PO description

The line items on your invoice should match the description and value on the PO.

Example:

PO says:

• Freelance graphic design services — brand refresh
• Value: £2,400 + VAT

Your invoice should say:

• Freelance graphic design services — brand refresh
• £2,400.00
• VAT @ 20%: £480.00
• Total: £2,880.00

Do NOT:

✗ Invoice for work not covered by the PO (this is a scope change — see next section)
✗ Change the description significantly (e.g. PO says "brand refresh" and you write "logo design and website mock-ups" — this may cause the invoice to be rejected)

If the work you did is slightly different from the PO description, check with the client before invoicing.

Sending the invoice: where does it go?

Check the PO document for the invoice submission address or portal.

Common scenarios:

1. Email to a specific address — E.g. "Send invoices to: accounts@nhstrust.nhs.uk" → Send the invoice PDF to that address, with the PO number in the email subject and body
2. Supplier portal — E.g. Tradeshift, Coupa, SAP Ariba, Amazon Business → Log in to the portal and upload your invoice, quoting the PO number
3. Client's finance team — The PO specifies a finance contact → Email the invoice to that person

Never send an invoice to the project contact (the person you did the work for) if the PO specifies a different invoice address. Invoices sent to the wrong address are delayed or lost.

Include the PO number in the email subject:

Subject: Invoice INV-2026-042 — PO-45892 — [Your business name]

Hi [Finance team],

Please find attached Invoice INV-2026-042 for freelance graphic design services (brand refresh) as per Purchase Order PO-45892.

Invoice amount: £2,880.00 (£2,400 + £480 VAT)  
Payment terms: Net 14 (due 29 October 2026)

Please let me know if you need any further information.

Thanks,  
[Your name]  
[Your business name]  
[Contact details]

When it goes wrong: common PO problems and how to fix them

Even if you follow all the steps, PO problems still happen. Here is how to fix the most common issues.

Problem 1: Invoice rejected for missing or wrong PO number

What happened:

You sent an invoice. Days or weeks later, you receive an email or automated message: "Invoice rejected. No valid purchase order number."

Possible causes:

✗ You forgot to include the PO number on the invoice
✗ You quoted the wrong PO (typo, or you used a PO from a previous project)
✗ The PO was cancelled or closed before you invoiced
✗ The client never raised a PO (you did the work without one)

How to fix it:

1. Contact the client immediately: "My invoice was rejected due to a missing/incorrect PO. Please can you provide the correct PO number?"
2. Cancel or credit the incorrect invoice: Mark the rejected invoice as VOID in your records. If required, issue a credit note (see credit note template UK for guidance).
3. Reissue a corrected invoice with the correct PO number: Use a new invoice number (e.g. if the original was INV-2026-042, the corrected invoice is INV-2026-043). State clearly in the email: "This replaces rejected invoice INV-2026-042."
4. Resend to the correct invoice address with the PO number in the subject line

Prevent it next time: Always get the PO before you start work, and double-check the PO number on your invoice before you send it.

Problem 2: PO value used up or scope grew

What happened:

You invoiced £3,000 but the PO value is only £2,400. The invoice is rejected because it exceeds the PO value.

Or: you completed additional work beyond the original scope (client asked for extra pages, revisions, or features) and you invoiced for the extra, but the PO does not cover it.

Why this is a problem:

POs are approval limits. The client's accounts system will not pay an invoice that exceeds the PO value, even if the work was done and approved by the project contact.

How to fix it:

1. Do NOT invoice for work beyond the PO value without a PO amendment or new PO.
2. Contact the client before you do extra work: "The original PO (PO-45892) covers £2,400 for the brand refresh. You have now asked for [additional work]. This is outside the original scope. Can you raise a PO amendment or a new PO for the extra £600?"
3. Wait for the client to amend the PO or raise a new PO.
4. Invoice the original scope against the original PO, and invoice the extra work against the new/amended PO.

Example:

• Original PO: PO-45892, £2,400 + VAT
• Invoice 1: INV-2026-042, £2,400 + VAT, quoting PO-45892 ✓
• Client requests extra work (£600 + VAT)
• Client raises new PO: PO-45910, £600 + VAT
• Invoice 2: INV-2026-043, £600 + VAT, quoting PO-45910 ✓

Prevent it next time: Agree scope clearly upfront. Use a scope of work document (see freelance scope of work template) and tell the client "Any changes to scope will require a new or amended PO."

Problem 3: PO expired or end date passed

What happened:

You finished the work and invoiced, but the PO has an expiry date or financial year-end date that has already passed. The invoice is rejected because the PO is closed.

Why this happens:

Public sector organisations often close POs at the end of the financial year (31 March for most UK public bodies). If you invoice after 31 March for work done before 31 March, the old PO may be closed and you need a new PO.

How to fix it:

1. Check the PO expiry date when you receive the PO (before you start work).
2. If the PO is close to expiry, ask the client: "This PO expires on 31 March. My invoice will be dated [April]. Can you extend the PO or raise a new PO for the new financial year?"
3. If the PO has already expired when you invoice, ask the client to raise a new PO or reopen the old one.

Prevent it next time: Invoice as soon as you complete the work. Do not wait weeks. If a project spans a financial year-end, ask the client upfront: "Will I need a new PO after 31 March?"

Problem 4: PO raised after the work

What happened:

The client asked you to start work urgently. You started without a PO (against your better judgment). The work is now complete, but the client is taking weeks to raise the PO and you cannot invoice.

Why this is a problem:

You have done the work, but you have no PO to quote on your invoice. The client's finance team will reject any invoice without a PO. You are at the client's mercy.

How to fix it:

1. Chase the PO politely but firmly: "I completed [project] on [date]. I cannot invoice without a valid purchase order number. Please can you provide the PO by [deadline]?"
2. Escalate if the client is unresponsive: Contact their finance or procurement team directly (if you have their details). Explain: "I was asked to start work without a PO. The work is complete and approved by [project contact]. I need a PO to raise my invoice."
3. If the client refuses to raise a PO, you may need to treat the work as disputed or write it off. Consult a solicitor or use debt recovery options (see letter before action template UK).

Prevent it next time: Never start work without a PO when the client operates No PO No Pay. If the client pressures you to start before the PO is raised, say no and explain the risk.

Problem 5: Client's PO terms differ from your terms

What happened:

You send the client your quote with a link to your standard terms of business (Net 14, liability cap, IP transfer on payment). The client raises a PO and sends it to you. The PO includes the client's own standard purchase terms (Net 90, no liability cap, IP transfers on delivery not payment, or an indemnity clause that makes you liable for the client's mistakes).

Why this is a problem:

If you accept the PO and start work, you may be agreeing to the client's terms, not yours. This is the battle of the forms problem in contract law. Whose terms govern? In many cases, the last set of terms sent before work begins wins.

How to fix it:

1. Read the PO terms carefully when the client sends you the PO.
2. If the PO terms conflict with your terms, do NOT accept the PO without flagging it. Email the client: "Thank you for PO-45892. I note that the PO includes your organisation's standard terms, which differ from my standard terms (linked in my original quote). Before I begin work, please confirm which terms apply to this project, or let's agree any changes in writing."
3. Agree in writing which terms govern. Options:
   • Your terms apply (the client agrees to waive their PO terms for this project)
   • The client's terms apply (you accept this, but only if you are comfortable with their payment terms, liability, and IP clauses)
   • Hybrid: your terms apply except for specific clauses that the client requires (e.g. you agree to their insurance requirements but keep your own payment terms)

For high-value or complex projects, consult a solicitor. Do not sign or accept a PO with terms you do not understand.

See also: Terms and conditions template UK for standard terms of business, and freelance contract template guide for project contracts.

Legal disclaimer: This is general information, not legal advice. Contract terms and the battle of the forms are complex. For large contracts or unfamiliar terms, seek professional legal advice.

Getting paid on time with a PO on your invoice

Once your invoice has a valid PO and is submitted correctly, payment should follow the client's stated payment terms (usually Net 30 for public sector, Net 14 or Net 30 for private companies).

The payment clock starts when a valid invoice is received

Important: For many organisations, the payment term (e.g. 30 days) starts from the date they receive a valid invoice, not from the date you send it.

Valid invoice = invoice with correct PO + correct value + correct format + sent to the correct address.

If your invoice is rejected and you resubmit it, the 30-day clock resets from the date they receive the corrected invoice.

Example:

• You send invoice on 1 October (no PO)
• Invoice rejected on 7 October
• You resubmit corrected invoice with PO on 10 October
• Payment clock starts 10 October, due 9 November (Net 30)

Lesson: Get the PO right the first time. Every rejection delays payment.

Chase politely if payment is late

If the payment due date passes and you have not been paid, chase politely.

Email template:

Subject: Payment reminder — Invoice INV-2026-042 (PO-45892)

Hi [Finance team / client name],

I hope you are well. I am writing to follow up on Invoice INV-2026-042 (dated 15 October 2026), which quoted your Purchase Order PO-45892.

The payment was due on 29 October 2026 (Net 14 days) and I have not yet received payment.

Invoice amount: £2,880.00  
Your PO: PO-45892  
Due date: 29 October 2026

Please can you confirm when I can expect payment?

If there is any issue with the invoice or if further information is needed, please let me know and I will address it immediately.

Thanks,  
[Your name]  
[Business name]  
[Contact details]

Send reminders at:

• Due date + 7 days (first polite reminder)
• Due date + 14 days (second reminder, firmer tone)
• Due date + 30 days (formal notice, mention late payment rights)

For full guidance on chasing late invoices, see how to chase a late invoice.

Your late payment rights (business clients only)

If the client is a business (not an individual consumer), you have legal rights under the Late Payment of Commercial Debts (Interest) Act 1998:

✓ Statutory interest: 8% per annum + Bank of England base rate, calculated daily from the due date
✓ Fixed compensation: £40 (invoices up to £999.99), £70 (£1,000-£9,999.99), £100 (£10,000+)
✓ Reasonable debt recovery costs: Solicitor fees, court costs (if legal action is required)

Important: The payment due date is the date stated on your invoice (e.g. Net 14 or Net 30), NOT the date on the PO. If your invoice says "Payment due 29 October 2026" and payment arrives on 15 November, you can charge late payment interest and compensation for the 17-day delay.

For full details, see statutory interest UK freelancers and invoice payment terms UK.

Note: Late payment rights do NOT depend on the PO. They apply to any business-to-business invoice. The PO is just the reference that allows the client's system to process the invoice. Your payment terms are set by you, not by the PO.

Worked example: freelance designer invoicing a council

Here is a step-by-step real-world example showing how a UK freelance designer handles a PO for a local council project.

Scenario:

Freelancer: Sam at Northline Studio (sole trader, not VAT registered)
Client: Riverside Borough Council (public sector, operates No PO No Pay)
Project: Design a series of public health campaign posters
Agreed fee: £2,400 (no VAT, as Sam is not VAT registered)
Date: October 2026

Step 1: Sam quotes £2,400 and asks about PO (1 October)

Sam sends the council a quote:

Subject: Quote for public health campaign posters — Northline Studio

Hi [Council contact],

Thanks for the opportunity to quote for the public health campaign poster designs.

**Quote:**

- Design of 4 A3 posters (public health campaign)  
- Supply files: print-ready PDF + editable AI files  
- Two rounds of revisions included  
- Fee: £2,400 (no VAT as I am not VAT registered)  
- Payment terms: Net 14 days from invoice date

Please confirm if you would like to proceed, and let me know if you need a purchase order for this work.

Full terms: [link to Sam's terms]

Thanks,  
Sam  
Northline Studio

Step 2: Council confirms PO is required (2 October)

The council replies:

Hi Sam,

We would like to proceed with your quote. Yes, we operate a No PO No Pay policy, so you will need to wait for the purchase order before you start work.

I have submitted the PO request to our procurement team. You should receive the PO by email within 3-5 working days.

Thanks,  
[Council contact]

Sam does not start work yet.

Step 3: Sam receives the PO and checks it (7 October)

On 7 October, Sam receives an email from the council's procurement team with a PDF attachment: Purchase Order PO/2026/4521.

Sam opens the PDF and checks:

✓ Supplier name: Northline Studio ✓
✓ Description: Design of 4 public health campaign posters ✓
✓ PO value: £2,400.00 ✓
✓ VAT: £0.00 (correct, as Sam is not VAT registered) ✓
✓ Payment terms: Net 30 days from receipt of valid invoice ✓
✓ PO number: PO/2026/4521 ✓
✓ PO expiry: 31 March 2027 ✓

Everything looks correct. Sam saves the PO PDF in a folder: Clients / Riverside Council / PO-2026-4521.pdf.

Sam replies:

Hi [Procurement team],

Thank you for Purchase Order PO/2026/4521. I have checked the details and everything is correct.

I will begin work this week and deliver the poster designs by 21 October.

Thanks,  
Sam  
Northline Studio

Step 4: Sam completes the work (21 October)

Sam designs the posters, sends them to the council contact, receives approval after one round of revisions, and delivers the final files on 21 October.

Step 5: Sam invoices the council, quoting the PO (21 October)

Sam creates Invoice INV-2026-078 with the following details:

INVOICE

Northline Studio  
14 Park Lane, Bristol, BS2 8QR  
Email: sam@northlinestudio.co.uk

Invoice Number: INV-2026-078  
Invoice Date: 21 October 2026  
Your PO Number: PO/2026/4521  
Payment Terms: Net 14 days  
Due Date: 4 November 2026

Bill to:  
Riverside Borough Council  
Civic Centre, High Street  
Riverside, RS1 2AB

Description:  
Design of 4 public health campaign posters (A3, print-ready PDF + AI files)  
As per Purchase Order PO/2026/4521

Amount: £2,400.00

Total Due: £2,400.00

Payment details:  
Sort code: 20-48-74  
Account number: 12345678  
Reference: INV-2026-078

Please pay within 14 days of invoice date. Late payment is subject to statutory interest and recovery costs under the Late Payment of Commercial Debts (Interest) Act 1998.

Sam emails the invoice to the address stated on the PO:

Subject: Invoice INV-2026-078 — PO/2026/4521 — Northline Studio

Hi [Finance team],

Please find attached Invoice INV-2026-078 for the public health campaign poster designs, as per Purchase Order PO/2026/4521.

Invoice amount: £2,400.00  
Payment terms: Net 14 days (due 4 November 2026)

Please let me know if you need any further information.

Thanks,  
Sam  
Northline Studio

Step 6: Payment arrives (28 October)

On 28 October (7 days after the invoice, 7 days before the due date), Sam checks the bank statement and sees:

Date: 28 Oct 2026  
Description: BACS — Riverside BC — INV-2026-078  
Amount: £2,400.00

Payment has arrived. Sam updates the invoice log:

Job done.

What Sam did right

✓ Asked about PO requirements upfront (in the quote email)
✓ Did not start work until the PO arrived
✓ Checked the PO carefully and confirmed it was correct
✓ Quoted the PO number on the invoice header (clear label: "Your PO Number:")
✓ Sent the invoice to the correct finance email address
✓ Included the PO number in the email subject line
✓ Got paid 7 days early (Net 14 terms, but paid in 7 days — common for councils when the invoice is clean)

PO checklist: before you start work and before you invoice

Use this checklist to avoid PO problems.

Before you start work:

✓ Ask the client: "Do you need a purchase order for this work?"
✓ If yes, ask: "Who raises the PO and when will I receive it?"
✓ Wait for the PO to arrive before you start work (unless you have a long-standing relationship and you trust the client to raise it within 48 hours)
✓ Check the PO when it arrives: your name, description, value, VAT, PO number, expiry date
✓ Query any errors immediately before you start work
✓ Save a copy of the PO in your client folder
✓ Note the PO number in your project notes or task tracker

Before you invoice:

✓ Confirm the PO is still valid (not expired or closed)
✓ Check the PO value covers your invoice amount (net + VAT)
✓ Quote the PO number exactly as it appears on the PO document
✓ Put the PO number in the invoice header, clearly labelled
✓ Match your invoice description to the PO description
✓ Check the invoice submission address (email or portal) on the PO
✓ Include the PO number in the email subject line when you send the invoice
✓ Keep a copy of the invoice and PO together in your records

Tracking PO invoices with SoloPad

Once you have the PO and you have invoiced the client, you need to track:

• Which invoice quotes which PO
• Whether the invoice was accepted or rejected
• When payment arrived
• If the client needs a new PO for the next phase or retainer invoice

SoloPad helps UK freelancers track invoices, client records, and payment status in one place.

How it helps with PO invoices:

✓ Record client PO numbers and notes against each project
✓ Track which invoices quote which POs (using invoice notes or reference fields)
✓ See payment status at a glance (awaiting payment, paid, overdue)
✓ Attach PO documents (PDF) to client records
✓ Set reminders to chase late payments

Pricing: Starter £5/month, Solo £12/month, Pro £29/month. 30-day free trial.

Try SoloPad free for 30 days.

Questions? info@solopad.io

Summary: get the PO, quote it right, get paid

PO numbers exist to control spending and match invoices to approvals. For freelancers, they are a necessary step in getting paid by NHS trusts, councils, universities, and large companies.

The process is simple:

1. Ask if a PO is required before you accept the job
2. Wait for the PO before you start work
3. Check the PO is correct (your name, value, VAT, expiry date)
4. Quote the PO number exactly on your invoice header
5. Send the invoice to the correct address with the PO in the subject line
6. Chase politely if payment is late

The cost of getting it wrong:

• Invoice rejected and returned unpaid
• Weeks of delay while you reissue a corrected invoice
• Cash flow problems
• Frustration and wasted admin time

The benefit of getting it right:

• Invoice processed and paid on time
• Professional relationship with the client
• No chasing, no disputes, no stress

Get the PO. Quote it right. Get paid.

Try SoloPad free for 30 days to track POs, invoices, and payments in one place.

Related guides

PO numbers are one piece of getting paid by large organisations. For the full picture, see:

• Invoice number UK — HMRC invoice numbering rules and how to set up your system
• Freelance invoice template examples — Copy-paste UK invoice templates with GBP, VAT, and sort code
• Invoice payment terms UK — Net 14, Net 30, due dates, and late payment rights
• How to chase a late invoice — Email scripts, statutory interest, and legal options
• Statutory interest UK freelancers — Your rights under the Late Payment of Commercial Debts (Interest) Act 1998
• Remittance advice UK — How to read and match payment notifications to invoices
• Credit note template UK — How to cancel or correct an invoice
• Freelance scope of work template — Define deliverables and boundaries to prevent scope creep
• Terms and conditions template UK — Standard terms of business to protect your payment rights
• Freelance contract template guide — Full project contracts for high-value work

Sources and references

This guide was written using the following official sources, public sector guidance, legislation, and keyword research:

1. NHS Property Services — Suppliers — No PO No Pay policy, Tradeshift portal, wait for valid PO before supplying (verified 15 October 2026)
2. Wirral Council — No Purchase Order No Pay Guidance — Policy in force since 1 April 2019, replacement invoice required with correct PO (verified 15 October 2026)
3. Renfrewshire Council — How we pay suppliers — PO required for all goods and services, 30-day payment from receipt of valid invoice (verified 15 October 2026)
4. RNOH NHS Trust — No PO No Payment policy from 1 April 2025 — Policy in line with most other NHS Trusts (verified 15 October 2026)
5. Late Payment of Commercial Debts (Interest) Act 1998 — Statutory interest and fixed compensation for late payment
6. GOV.UK — Late commercial payments: charging interest and debt recovery — Official guidance on late payment rights
7. GOV.UK — Invoices: what they must include — Invoice requirements including unique identification number
8. Ubersuggest UK keyword data (location ID 2826, 15 October 2026): "po number" (1,300/mo, SD 21), "what is a purchase order" (3,600/mo, SD 24), "purchase order number invoice" (320/mo, SD 15), "what is po number in invoice" (260/mo, SD 20), "how to get a purchase order" (260/mo, SD 23), "invoice purchase order number" (260/mo, SD 17), "purchase order and invoice" (210/mo, SD 16)

Method note:

SERP competitors reviewed (not copied): Sage UK glossary (buyer-side definition), GoCardless blog (generic explainer), Howden insurance guide (buyer perspective), Amazon Business supplier help (platform-specific), Ramp finance guide (US-focused), HighRadius blog (accounts payable software vendor), Stripe AU invoicing guide (Australian audience), Reddit threads (user questions, no structured guidance). None of these sources provide a UK supplier-side guide covering: No PO No Pay policies with real NHS/council citations, step-by-step supplier workflow (how to get a PO before work starts), exact invoice placement and format rules, fixes for rejected invoices, scope and PO amendment process, or the battle of the forms risk when PO terms conflict with freelancer terms.

All examples (Sam at Northline Studio, Riverside Borough Council, email templates, invoice wording, PO/2026/4521), decision tests, checklists, and supplier-side explanations are original SoloPad editorial content. All NHS and council policies cited are real and verified via the linked pages (October 2026).

This article is for general education. It is not legal, tax, or accounting advice. Purchase order processes, No PO No Pay policies, payment terms, and late payment rights may vary by organisation, contract, and jurisdiction. When in doubt, consult an accountant, solicitor, or the client's finance team directly.