How to create a purchase order: a definitive guide for UK businesses

Key takeaways

• A purchase order, also known as a PO, is a legally binding document that is given to a seller from the buyer, that specify what you're buying, and at what price.

• Businesses must implement PO processes so they can avoid "maverick spending", i.e. unauthorised purchases that go outside the proper channels. Compliance gaps can cause issues with HMRC later on, so an airtight PO process is crucial for every business.

• Spreadsheet templates can handle basic PO creation, but Airwallex adds the financial infrastructure layer they lack — multi-currency accounts, automated bill pay at interbank FX rates, and local payment rails in 150+ countries — so UK businesses with international suppliers can settle POs globally, avoid high FX fees from traditional banks, and cut cross-border payment costs by up to 90%.

Managing company spending without a formal process in place is one of the most common causes of budget overruns. Purchase orders (PO) establish what is being sold or provided, and at an agreed price. Without them, there's no agreed price on record, no approval trail, and nothing to reference back to if a dispute arises.

If you don't get a PO process sorted, you can expect duplicate payments, incorrect VAT treatment, and a month-end close that drags on far longer than it should. If you're a founder or part of a finance team, it just means another headache. But, it doesn't have to be that way.

This guide covers what a purchase order is, what it needs to include to be legally robust in the UK, and how to build a procurement process that works — from first requisition through to payment.

What is a purchase order?

A purchase order (PO) is a type of document sent from a buyer to a supplier to request goods or services, that agree on what is being sold, and at what price.

POs act as a legal record. Once a supplier accepts a PO — either in writing or simply by fulfilling the order — it becomes a legally binding contract under UK law. If a dispute arises over quantity, price, or delivery, the PO is your first line of defence and creates a paper trail that provides proof of agreed terms.

They also give you budget control. A PO allows your finance team to track upcoming stock, or whatever it is they might be tracking, and ensure spend stays within authorised limits before a single penny leaves the account. So, cash-flow forecasting becomes significantly more accurate and helps prevent maverick spend — unauthorised purchases that bypass your approvals process and chip away at your budget without anyone noticing.

And, for growing businesses, POs are often essential for winning and retaining larger customers. Many UK councils, NHS trusts, and large corporates won't process an invoice without a valid PO number. Without one, your invoice gets returned or placed on hold.

While not legally required for every transaction, using POs provides professional credibility, better record-keeping, and legal protection that becomes increasingly essential as a business scales.

Benefits of using purchase orders

For many UK businesses, a PO can feel like an extra administrative step. But, the returns — in legal protection, budget control, and supplier credibility — significantly outweigh the time it takes to raise one.

Legal protection and dispute resolution: Once a supplier accepts your PO, it becomes a legally enforceable contract under UK law. If a dispute arises over what was ordered, at what price, or by when — the PO is your evidence. Without one, you're relying on email threads and verbal agreements that are far harder to enforce.

Budget control and spend visibility: A PO commits spend on your books the moment it's approved — before any cash leaves the account. That means your finance team can track upcoming costs in real time, ensure every purchase is authorised against the right cost centre, and prevent maverick spend from eroding budget without anyone noticing.

Stronger supplier relationships and procurement credibility: Operating a consistent PO process signals to suppliers that you're a reliable, organised buyer. It also makes you eligible to trade with larger customers. Many UK councils, NHS trusts, and large corporates operate strict "No PO, No Pay" policies— meaning businesses without a formal PO process can find themselves locked out of public sector and enterprise contracts.

Better record-keeping and compliance: A digital PO trail satisfies HMRC's expectations for purchase records and makes VAT reconciliation, audit preparation, and month-end close significantly faster. The more consistent your PO process, the cleaner your books — and the less time your finance team spends chasing paperwork when it matters most.

What a purchase order needs to include

If you're putting together a purchase order, it needs to contain the following:

The unique PO number deserves particular attention. It's a unique alphanumeric identifier assigned by the buyer that ties together the PO, the goods received note (GRN), and the supplier's invoice — the three documents your accounts team compares to authorise payment.

Without a PO number on the invoice, three-way matching breaks down, and the risk of overpayment or fraud rises sharply.

For the itemised order list, make sure each line includes:

• A clear description of the goods or service being ordered

• The SKU or item code (where applicable)

• Quantity and agreed unit price

• The line total (quantity × unit price)

Getting these fields right from the start keeps your accounts payable process moving without unnecessary delays or supplier queries.

How to create a purchase order: the six-step process

Most businesses follow the same cycle, from internal request to payment authorisation:

1. Raise a purchase requisition. A team member identifies a need and submits an internal request for approval. This confirms budget availability before any external commitment is made.

2. Create the PO. Using your template or spend management software, generate the PO with all the required fields and assign a unique PO number.

3. Internal approval. A budget owner or finance lead reviews the PO for price accuracy, correct cost-centre coding, and business necessity before it's authorised and sent out.

4. Send to the supplier. Once approved, the PO goes out by email or through a digital procurement portal. This is your formal request to proceed with the order.

5. Supplier acceptance. The supplier confirms the terms — in writing or by beginning fulfilment. At this point the PO becomes a binding agreement.

6. Three-way matching and payment. When the invoice arrives, match it against the PO and the GRN. If all three documents agree, the invoice clears for payment. Any discrepancy is flagged before money leaves the account.

This six-step cycle is what separates businesses with clean procurement records from those constantly firefighting invoice queries at month-end. Even a lightweight version of this process — requisition, PO, approve, send, accept, match — makes a meaningful difference to spend control.

The four types of purchase order

Different purchasing scenarios call for different structures. The four most common types in UK practice are:

Choosing the right type from the start reduces renegotiation, simplifies forecasting, and keeps supplier relationships stable. Many UK businesses start with standard POs and introduce blanket POs as supplier partnerships mature and purchase volumes increase.

Purchase order vs. invoice: what's the difference?

Purchase orders and invoices might seem similar, but they serve opposite functions in a transaction.

A purchase order comes from the buyer and arrives at the start of the deal — before goods or services change hands. It authorises the transaction and sets the agreed terms. An invoice comes from the seller and arrives after delivery — it's a formal request for payment.

The two documents are designed to mirror each other. When a supplier quotes the correct PO number on their invoice, your accounts payable team can reconcile both documents quickly — cutting the risk of duplicate payments, pricing mismatches, and fraud before any funds are released. That's why insisting on a PO number is such a simple but effective financial control.

Modern procurement software takes this further. A "PO flip" lets a supplier convert a digital PO into an invoice in a single click, cutting manual data entry and ensuring the invoice mirrors the approved PO exactly— eliminating a common source of discrepancy before it even reaches your team.

When to move beyond spreadsheet templates

Most businesses start with Word or Excel PO templates. That works at very small scale, but manual processes quickly become a liability as order volumes and supplier numbers grow.

Chasing approvals over email, re-keying invoice data, and manually reconciling documents at month-end all add up. When POs are logged digitally and approved before an invoice arrives, finance teams see committed spend in real time rather than discovering it weeks later at invoice stage. Digital systems also make it much easier to require a PO for every invoice, so your team isn't chasing retroactive approvals or rejecting invoices that can't be matched.

Moving to a unified platform gives you:

• Automated invoice matching. AI-powered extraction matches invoices to POs without manual data entry, flagging discrepancies in quantity, price, or VAT before money leaves the account.

• Real-time cash flow visibility. Committed costs are visible the moment a PO is approved — before cash even leaves the account.

• Built-in audit trails. Digital approval workflows satisfy HMRC's record-keeping requirements automatically.

For UK businesses with international suppliers, the stakes are higher still. Manual procurement processes contribute to significant delays in cross-border payment cycles — global firms using manual processes experience up to a 33% delay in international payments— compounding slower reconciliation with avoidable FX conversion costs on top.

Connecting your PO process directly to multi-currency accounts and cross-border payment rails allows you to manage currency, timing, and settlement in one flow rather than patching together spreadsheets and bank portals.

Airwallex links POs directly to multi-currency wallets, so you avoid the high FX fees that traditional banks typically charge every time you settle a foreign-currency PO. Bill pay and accounts payable automation workflows let you connect approved invoices to their matching POs, route them for sign-off, and schedule payments over local rails. And, virtual cards tied to department-level budgets ensure employee spend stays inside PO-approved limits before it ever hits the P&L.

When PO creation, approval, three-way matching, and payment all sit in the same platform, reconciliation that once took days can take minutes.

Procurement made simple with Airwallex

A purchase order isn't just paperwork. It's the document that protects your cash flow, enforces your budget, and builds the audit trail HMRC expects as your business grows.

Start with a clear template that covers all the core fields. Build a six-step approval process your team follows consistently. And when manual workflows start to slow you down, move to a platform that automates matching, approvals, and payment in one place.

Airwallex gives UK businesses the tools to manage the full procurement cycle — from PO creation through to multi-currency payment — without the cost and complexity of traditional banking. Open a business account to take control of your procurement spend.

Frequently Asked Questions (FAQs)

Is a purchase order legally binding in the UK?

Yes. Once a supplier accepts a PO — either in writing or by beginning to fulfil the order — it becomes a legally binding contract under UK law. Both parties are then obligated to honour the agreed terms: the supplier to deliver, and you to pay on the agreed timeline.

Who generates the purchase order number?

The buyer generates the PO number at the point of creation. It's a unique alphanumeric identifier assigned to track the order through the full procurement cycle. If you're the supplier in a transaction, always ask for your customer's PO number before issuing an invoice — without it, payment can be withheld under a "No PO, No Pay" policy.

Do small businesses need purchase orders?

There's no legal obligation for every UK business to use POs. But, consistent use of POs builds the spend management discipline that makes tax preparation and month-end reconciliation significantly less painful as you scale. Even a basic template and a simple approval step can make a real difference.

What is three-way matching?

Three-way matching is the process of comparing a purchase order, a goods received note (GRN), and a supplier invoice to confirm all three agree before payment is released. It's one of the most effective controls for preventing overpayments and invoice fraud in any UK procurement process.