How to Verify UK VAT Numbers Before Paying Invoices (Step-by-Step Guide)

Paying a UK invoice without confirming the supplier's VAT number is one of the most common ways finance teams lose money to fraud and enter the wrong tax on a VAT return. A number that "looks right" can still be invalid, deregistered, or registered to a different business. This guide walks accounts payable teams through a repeatable workflow to verify any UK VAT number against HMRC's live register before payment is released.

Why verifying a VAT number protects your business

When you pay a VAT-inclusive invoice, you trust that the supplier is genuinely VAT-registered so you can reclaim the input tax. If the number is invalid, HMRC can reverse your input tax claim, levy a penalty, and ask you to account for the VAT again. In "missing trader" or carousel fraud, the supplier may have used a real but stolen number, or one deregistered weeks earlier. The cost is not just tax — paying a fraudulent supplier means goods may never arrive, and recovery against a dissolved company is rarely successful. A 30-second check before payment is the cheapest control you can implement.

The UK VAT number format, explained

A standard UK VAT number is nine digits, often written with a "GB" prefix and grouped with spaces, e.g. GB 123 4567 89. The rules that matter:

• The core number is always nine digits and can begin with a zero.
• The "GB" prefix is optional for domestic trade but required in some cross-border contexts; "XI" is used for Northern Ireland traders in certain EU schemes.
• Grouping (5+4 or 3-3-3) is presentation only and does not change the underlying number.
• A 12-digit number beginning "GD" or "HA" is a Government Department or Health Authority identifier, not a trader number.

Always strip spaces, dashes and the "GB" prefix before checking.

A built-in checksum to sanity-check first

Before querying HMRC, run a lightweight checksum that catches most transcription errors. Multiply the first eight digits by the weights 8, 7, 6, 5, 4, 3, 2, 1, sum the results, add 55, then take modulo 97. If the result equals the ninth digit, the number is structurally plausible. This catches single-digit typos and most transpositions instantly — but it does not prove the number is registered. Always follow it with a live HMRC lookup for any meaningful payment.

Step-by-step: verify a VAT number before payment

1. Extract the number from the invoice exactly as printed.
2. Normalise it. Remove the "GB" prefix, spaces and dashes to leave nine digits. If not nine digits, request a corrected invoice.
3. Run the checksum above. If it fails, the number is mistyped — contact the supplier.
4. Perform a live HMRC lookup. Query the official HMRC VAT lookup service in real time. You can do this instantly and free at the top of this page — enter the nine digits and receive the registered business name and address.
5. Cross-check name and address. The HMRC name should match the supplier (minor formatting differences are fine). The registered address should be consistent with where the supplier operates. A number registered to a flat in a different city is worth one phone call.
6. Record the result. Save the date, VAT number, registered name and the HMRC consultation reference in your AP file as audit evidence.
7. Decide and pay. If consistent, release payment; if not, hold and contact the supplier.

Common fraud signals

• The VAT number is valid but registered to a company that has since dissolved — always pair the VAT check with a Companies House status check.
• The registered name bears no resemblance to the supplier you trade with, suggesting a stolen number.
• The supplier becomes evasive when asked for the VAT number in writing.
• The number was registered days before a large invoice, a sign of a fresh shell entity.

Making it routine

Build VAT verification into the invoice approval workflow rather than treating it as an exception. For invoices above a threshold you set (e.g. £1,000), require a fresh live lookup saved against the invoice record. For volume processing, a bulk verification tool can check hundreds of numbers in one run and export a CSV to match against your purchase ledger. Verifying a VAT number is the difference between reclaiming input tax cleanly and discovering months later that HMRC has disallowed a six-figure claim.