Purchase Orders for Trade Businesses UK 2026 — A Practical Guide to Controlling Material and Subcontractor Spend

What Is a Purchase Order?

A purchase order (PO) is a document you raise and send to a supplier to confirm exactly what you want to buy, at what price, and for which job. It is your instruction to the supplier: "I am ordering these items, at these agreed prices, deliver them here." Once the supplier accepts it, a PO becomes a record of what was agreed before any goods change hands or any money is owed.

The key thing about a PO is the direction it travels and the moment it happens. You raise it, you send it to the supplier, and you do it before the goods arrive. That timing is what makes it useful — it locks down the price and quantity in writing, so when the delivery and the invoice turn up later you have something firm to check them against.

PO vs Invoice vs Quote — What's the Difference?

These three documents get muddled constantly on site, but they do completely different jobs. A quote is what you give a customer. An invoice is a demand for payment. A purchase order sits between them, on the buying side of your business.

Put simply: a quote is you offering work, a purchase order is you ordering supplies, and an invoice is somebody asking to be paid. A PO comes before the supplier's invoice and is the thing that invoice should be checked against. If a supplier's invoice doesn't match the PO, you have a question to ask before you pay — and that question is often worth real money.

Why Purchase Orders Matter for Trades

Plenty of trade businesses run for years without ever raising a formal PO, so it's fair to ask what the point is. The answer is control. A PO turns a casual phone order into a checkable record, and that record protects you in several specific ways.

• Controlling spend: When every order has to be raised against a job, you can see committed costs before the invoices land. You know what you've ordered and what it will cost, rather than finding out at month-end when the merchant statement arrives.
• Matching deliveries and invoices to what you actually ordered: A PO gives you a baseline. When the goods and the supplier invoice arrive, you can check both against it instead of taking the supplier's word for the quantity and price.
• Accurate job costing: Every PO carries a job reference, so material and subcontractor costs land against the right job automatically. That is the foundation of knowing which jobs actually made money — and which only looked like they did.
• Not paying for what you didn't receive: Short deliveries, missing items and over-charges are common. A PO is the evidence that lets you challenge an invoice with confidence rather than a vague memory of the phone call.
• Controlling who can order: Trade accounts at merchants are easy to abuse — anyone with the account number can put materials on them. Requiring a PO for orders above a certain value stops staff, apprentices and subcontractors quietly racking up spend you never authorised.

Every one of these ties back to the same two things: your margin and your cash flow. Trade margins are tight enough that a few percent of unchecked over-charging across a year is the difference between a profitable quarter and a flat one. And paying invoices you never checked is paying out cash you didn't need to spend yet.

The Simple Purchase Order Process

You do not need a procurement department to run POs. The whole process is four steps, and most of it can be done from your phone on the way to site.

• 1. Raise the PO. Before you order, create a purchase order with the supplier's details, the items and quantities you want, the prices you've agreed, and — crucially — the job reference the order is for. Send it to the supplier.
• 2. Goods delivered with a delivery note. When the materials arrive, the driver hands over a delivery note listing what is in the load. Check the goods against the note before signing — count the items, look for damage, and note anything short or wrong on the note itself.
• 3. Supplier invoice arrives. Days or weeks later, the supplier sends an invoice asking for payment. This is the document that takes money out of your business.
• 4. Three-way match before paying. Before you pay, line up three documents: the PO (what you ordered), the delivery note (what actually turned up), and the invoice (what you're being asked to pay). All three should agree. If they do, pay it. If they don't, you've caught a problem before it cost you anything.

That final step — the three-way match — is where the value of the whole system lives. It is a thirty-second check that catches short deliveries, price creep and double-billing before the money goes out. Without it, you are effectively trusting that every supplier invoice is correct, and over a busy year that trust will cost you.

What a Purchase Order Should Contain

A PO only works if it has enough detail to check against later. Skimp on it and the three-way match falls apart. Keep it simple, but make sure every PO carries the following.

The agreed price field is the one trades most often leave blank, and it's the one that catches over-charging. If your PO says £18 a sheet because that's what you negotiated, and the invoice comes in at £22 a sheet, the gap is obvious. Without the agreed price written down, you're relying on memory against a printed invoice — and memory loses that argument every time.

Using POs With Merchant Trade Accounts

Merchant trade accounts are convenient and dangerous in equal measure. The convenience is that anyone you send to the counter can collect materials on the account. The danger is exactly the same thing — anyone can. Without a PO discipline, your trade account becomes an open tab that staff, apprentices and the occasional opportunist can all add to, and you only see the total weeks later on the statement.

Requiring a PO for account orders above a set threshold solves this. The rule is simple: no PO, no order. It forces a moment of authorisation before the spend happens, and it gives you a job reference for everything that goes on the account. When the monthly statement arrives, you reconcile it line by line against your POs — anything on the statement without a matching PO is a question for whoever ordered it.

This also makes your end-of-month far less painful. Instead of guessing which jobs the merchant spend belongs to, every line is already allocated. Your job costing is accurate, your statement reconciliation is quick, and the days of staring at a merchant statement trying to remember what "sundries" was for are over.

Using POs With Subcontractors

Purchase orders aren't only for materials. Subcontractor labour is one of the biggest variable costs on larger jobs, and it's just as prone to disputes — usually over what was agreed versus what gets invoiced. A PO raised to a subcontractor pins down the scope, the day rate or price, and the job it relates to before they start.

When the subbie's invoice comes in, you check it against the PO the same way you check a material invoice against a delivery note. Did they invoice the agreed rate? Is it allocated to the right job? Are there extras that were never authorised? A PO turns "I think we said three days at this rate" into a document you both signed up to. It protects the relationship as much as the margin — clear terms up front mean fewer awkward conversations at invoice time.

Subcontractor POs also feed straight into your job costing. Labour and materials both land against the same job reference, so when you look at whether a job made money, you're seeing the full cost picture rather than just the bits that happened to get recorded.

Paper, Spreadsheet or Software?

You can run POs on paper, in a spreadsheet, or in software, and the right answer depends on your volume. The important thing is that you run them at all — even a basic system beats no system.

• Paper PO book: A duplicate-pad PO book costs a few pounds and works for very low volumes. The downside is that the records sit in a van or a drawer, the three-way match is manual, and job costing means typing it all up later anyway.
• Spreadsheet: A shared spreadsheet with one row per PO is a clear step up — it's searchable, you can total spend by job, and it costs nothing. The weakness is discipline: it only works if everyone updates it, and it doesn't connect to your invoices, so the three-way match is still manual.
• Software: Job management software raises POs against a job, links them to the delivery and the supplier invoice, and flags mismatches automatically. The cost allocation to the job happens for you, so your job costing and your margin figures stay accurate without extra admin.

For a sole trader doing a handful of orders a week, a spreadsheet is fine. As you grow — more staff ordering, more accounts, more jobs running at once — the manual matching becomes the bottleneck, and that's the point where software pays for itself. The win isn't the PO document; it's having every material and labour cost land on the right job without anyone having to retype it.

Frequently Asked Questions

Do small trade businesses really need purchase orders?

If you only do a few small jobs a month and buy materials yourself, you can probably manage without a formal system. The moment you have staff ordering on a trade account, use subcontractors, or run several jobs at once, POs start saving you more than they cost. The trigger is usually when you stop being able to remember what was ordered for which job off the top of your head.

What's the difference between a PO number and an invoice number?

A PO number is your reference for an order you placed. An invoice number is the supplier's reference for a bill they sent you. Asking the supplier to quote your PO number on their invoice is what lets you match the two quickly. They are separate references created by separate parties for separate documents.

What is a three-way match?

It's the check you do before paying a supplier invoice: compare the purchase order (what you ordered), the delivery note (what arrived), and the invoice (what you're billed). When all three agree, you pay with confidence. When they don't, you've found a short delivery, an over-charge or a billing error before any money left your account.

Can I raise a purchase order to a subcontractor?

Yes. A PO works just as well for labour as for materials. Raise it with the agreed rate or price and the job reference, and check the subcontractor's invoice against it the same way you'd check a merchant invoice. It sets clear expectations and keeps labour cost allocated to the right job.

How does a PO help my job costing?

Because every PO carries a job reference, the cost of those materials or that labour attaches to a specific job from the moment it's ordered. That means when you review whether a job made money, you're looking at its true cost — not an estimate, and not a figure missing the bits nobody wrote down.

The Bottom Line

Purchase orders are not bureaucracy — they're a margin tool. In a trade where materials and subcontractors are the bulk of your costs, a simple PO system means you only pay for what you ordered, at the price you agreed, on the job it belongs to. The three-way match catches the small over-charges and short deliveries that would otherwise vanish into your monthly statement, and accurate job costing tells you which work is genuinely worth doing again.

Start with one rule — no PO, no order above a set value — and a job reference on everything. Whether you use a spreadsheet or software, that discipline alone will tighten your margins and steady your cash flow more than almost any other piece of back-office admin you could put in place.