A purchase order (PO) is a formal document issued by a buyer to a seller that specifies the goods or services being ordered, agreed quantities, prices and delivery terms. In UK business practice, purchase orders are a cornerstone of structured procurement and effective financial control.
Why purchase orders matter
Without purchase orders, businesses have limited visibility over committed spending. POs provide:
- Authorised spending with documented approval before the commitment is made
- Budget control by tracking committed costs against available budget
- Clear communication of exactly what is being ordered and on what terms
- Legal protection as the PO forms part of the contract between buyer and seller
- Audit trail connecting the purchasing decision to the invoice and payment
For smaller businesses, purchase orders can feel like unnecessary paperwork. But as transaction volumes grow, the lack of a PO process is one of the most common causes of overspending, duplicate payments and disputes with suppliers.
The purchase order process
1. Requisition
A team member identifies a need and submits a purchase requisition, an internal request that describes what is needed, the estimated cost and the business justification. This is an internal document and does not go to the supplier.
2. Approval
The requisition goes through an approval workflow based on the organisation’s spending authority matrix. This might involve:
- Line manager approval for amounts under a certain threshold
- Finance team review for budget availability
- Director or board approval for high-value commitments
3. Purchase order creation
Once approved, the procurement or finance team creates a formal purchase order containing:
| Field | Detail |
|---|---|
| PO number | Unique sequential identifier |
| Date | Date the PO is issued |
| Buyer details | Company name, address, contact |
| Supplier details | Company name, address, contact |
| Delivery address | Where goods should be delivered |
| Item descriptions | Detailed description of goods or services |
| Quantities | Number of units or scope of services |
| Unit prices | Agreed price per unit or total for services |
| Total value | Sum of all line items |
| VAT | Applicable VAT rates and amounts |
| Payment terms | See payment terms |
| Delivery date | Expected delivery date |
| Terms and conditions | Standard purchasing terms |
4. Dispatch to supplier
The PO is sent to the supplier, who reviews it and either accepts, queries or rejects it. Acceptance of a PO by the supplier creates a binding contract for the supply of the specified goods or services.
5. Fulfilment and receipt
The supplier delivers the goods or performs the services. The buyer verifies that what was received matches the PO through a goods receipt or service completion process.
6. Invoice matching
The supplier sends an invoice referencing the PO number. The buyer’s finance team matches the invoice against the PO and goods receipt before approving payment.
Legal status of purchase orders
In UK contract law, a purchase order typically constitutes an offer to buy. When the supplier accepts the PO (explicitly or by fulfilling the order), a contract is formed. Key legal points:
- The PO’s terms and conditions form part of the contract
- If the supplier’s terms conflict with the buyer’s PO terms, the battle of the forms doctrine applies, and the last set of terms communicated before performance generally prevails
- Verbal orders without a written PO are harder to enforce in disputes
- POs can be amended by mutual agreement, creating a PO amendment or revised PO
Three-way matching
Three-way matching is the process of comparing three documents before approving an invoice for payment:
- Purchase order showing what was ordered and at what price
- Goods receipt note (GRN) confirming what was actually delivered
- Invoice detailing what the supplier is charging
All three must align within acceptable tolerances before the invoice is approved. Discrepancies trigger investigation:
| Discrepancy | Possible cause | Resolution |
|---|---|---|
| Invoice amount exceeds PO | Price increase, extra charges | Query supplier, amend PO or request credit note |
| Quantity received differs from PO | Short delivery, damaged goods | Adjust GRN, request credit note |
| Invoice references wrong PO | Supplier error | Return to supplier for correction |
| GRN not completed | Goods not yet inspected | Hold invoice until receipt confirmed |
This control prevents paying for goods not received, quantities not ordered or prices not agreed.
Purchase orders and budgeting
POs play a critical role in commitment accounting, where spending is tracked from the point of commitment (PO raised) rather than the point of payment (invoice paid):
- Available budget = Approved budget minus committed POs minus paid invoices
- This prevents budget overspends caused by orders that have been placed but not yet invoiced
- Finance teams can report on committed costs alongside actual costs for a complete picture
For a broader view of how this fits into financial management, see what accounting is.
Types of purchase orders
Standard purchase order
A one-off order for specific goods or services with defined quantities, prices and delivery dates.
Blanket purchase order (framework order)
An agreement covering multiple deliveries over a period, typically with:
- Agreed unit prices or rate card
- Maximum total value
- Defined period (e.g. 12 months)
- Deliveries called off as needed via release orders
Blanket POs are common for recurring supplies like office materials, maintenance services or raw materials.
Contract purchase order
Used alongside a formal contract for complex or high-value engagements, where the PO references the contract terms rather than restating them.
Scheduled purchase order
Similar to a blanket order but with pre-agreed delivery dates and quantities, useful for manufacturing and supply chain planning.
Purchase orders in accounting
When the PO is raised
No accounting entry is required, but the committed amount should be tracked in the procurement or budgeting system for commitment reporting.
When goods are received
Debit: Stock / Work in progress / Expense
Credit: Goods received not invoiced (GRNI) accrual
When the invoice is received and matched
Debit: GRNI accrual
Credit: Trade payables
When payment is made
Payment is typically made via BACS, Faster Payments or CHAPS depending on the amount and urgency:
Debit: Trade payables
Credit: Bank
Common mistakes with purchase orders
- Raising POs after the fact (retrospective POs) which defeats the purpose of pre-approval
- Not closing completed POs which inflates committed spend in reports
- Vague descriptions that make three-way matching difficult
- Skipping the PO process for low-value purchases without defining a sensible threshold
- Not referencing PO numbers on invoices which slows down payment processing
PO-based vs non-PO-based procurement
Not every purchase needs a formal PO. Many businesses define a threshold below which purchases can be made without a PO (for example, under £250). Above that threshold, a PO is mandatory.
| Approach | When to use | Risk |
|---|---|---|
| PO-based | Higher value, formal suppliers | Low risk, strong controls |
| Non-PO (expense claim) | Low value, ad hoc purchases | Moderate risk, less oversight |
| Corporate card | Travel, subscriptions, small items | Moderate risk, needs receipt reconciliation |
The threshold should balance control with efficiency. Setting it too low creates bureaucratic overhead; setting it too high undermines financial discipline.
Purchase orders and proforma invoices
A proforma invoice often precedes the purchase order in the buying cycle. The buyer receives a proforma from the supplier, uses it to justify and raise a PO, and then sends the PO back to the supplier to confirm the order.
This sequence provides a complete procurement trail: quotation or proforma, followed by PO, followed by delivery, followed by invoice, followed by payment.