Checking a UK VAT number takes ten seconds. Doing it in a way that protects you takes eleven.
The difference is one field on the form, and almost nobody explains it.
HMRC's service confirms whether a GB VAT number is valid and returns the name and address of the business it belongs to. If you also enter your own VAT number, it records the check and gives you documented evidence of when you made it.
That record is the point. This is how to run the check properly, how to sanity-check a number before you even open the service, and why an EU checker will tell you a perfectly valid British number does not exist.
The official service, and what it does
The check runs at gov.uk/check-uk-vat-number. It is free, available in English and Welsh, and needs no account.
| It does | It does not |
|---|---|
| Confirm a UK VAT number is valid | Search by business name |
| Return the registered name and address | Check EU VAT numbers |
| Record your check, if you supply your own VAT number | Work while your own registration is pending |
Two limits catch people out.
You must already have the number. There is no name lookup. HMRC's guidance points you at the obvious sources: "You can find the VAT numbers for most businesses and organisations on their invoices, receipts or website."
It is unavailable while your own registration is being processed. If you have applied and are waiting on HMRC, you cannot use the proof function until they come back to you.
The field that turns a check into evidence
The service has an optional second field for your own VAT registration number.
Fill it in, and HMRC records that you performed the check and when. Leave it blank, and you get the same answer with no trace that you ever asked.
Returns: valid, business name, address.
- Confirms the number on screen
- No consultation reference
- Nothing to show later that the check happened
Returns: valid, business name, address, and a reference.
- Same confirmation on screen
- Timestamped proof that you checked
- Costs one extra field and no extra time
Why it matters: if a supplier's VAT registration turns out to be invalid or fraudulent, the question that follows is what you did to check. Being able to show the date on which you verified the number is a materially different position from asserting that you did.
Run the check when you onboard a supplier, and again if anything about the relationship changes.
The four UK VAT number formats
Most guides give you one. There are four, and the last two still turn up on historical invoices.
| Format | Structure | Who uses it |
|---|---|---|
| Standard | GB + 9 digits, e.g. GB123456789 | Most businesses |
| Branch trader | GB + 9 digits + 3 digit branch identifier, 12 digits total | Businesses registered with branch traders |
| Government department | GB + GD + 3 digits, 000 to 499 | UK government departments |
| Health authority | GB + HA + 3 digits | Health authorities |
The GD and HA formats are increasingly rare. If one appears on an invoice and your validation tool
rejects it as malformed, the tool is wrong, not the invoice.
Checking a number without a lookup
Every genuine UK VAT number carries a built-in check digit, calculated with a modulus 97 formula. You can test it offline.
The published method for a standard nine digit number:
- take the first seven digits
- multiply them by the weights 8, 7, 6, 5, 4, 3, 2 respectively
- add the results
- add the last two digits, the check digits
- the total must be divisible by 97
Older numbers issued before a certain date use a variant, sometimes called modulus 9755, so a failed check on a very old number is not conclusive on its own.
This is a sanity check, not a verification. It tells you a number is structurally impossible. It cannot tell you a structurally valid number belongs to the business claiming it, or that the registration is still live. For that you need HMRC.
Where it earns its keep: catching typos before you file, and screening a list of numbers before you spend time checking each one individually.
The VIES trap
This is the most common practical mistake since Brexit, and it produces a false negative that looks like fraud.
Great Britain is outside the EU VAT Information Exchange System. A normal GB VAT number will not validate in VIES. Not because it is fake, but because Great Britain is no longer in the system that VIES queries.
Northern Ireland is different. Under the Windsor Framework, which replaced the Northern Ireland
Protocol, Northern Ireland businesses trading goods with the EU use an XI prefix. XI numbers
follow the same nine digit structure, and they do validate through VIES.
| Number | Check it here |
|---|---|
GB + 9 digits | HMRC, gov.uk/check-uk-vat-number |
XI + 9 digits | VIES, the EU system |
| Any EU member state number | VIES |
| HMRC checker | VIES | |
|---|---|---|
| Starts with GB | Use this | Great Britain left VIES |
| Starts with XI | Northern Ireland, Windsor Framework, goods with the EU | |
| Any other EU country code | Use this |
What to do when a number does not validate
Work through it in this order, because the innocent explanations are far more common than the guilty one.
Check the transcription. A single wrong digit fails. Compare against the source document rather than against what you typed.
Check the format. A branch trader number has twelve digits. Stripping the last three because a form expected nine will fail every time.
Check the system. A GB number in VIES fails by design. An XI number in HMRC's checker may not behave as you expect either.
Check the timing. A registration that has been cancelled, or one that has not yet been issued, will not validate. Newly registered businesses sometimes quote a number before it is live.
Then ask the supplier. Give them the specific result. A legitimate business will resolve it in a phone call. A supplier who cannot produce a valid registration while charging you VAT is a supplier you should not be paying VAT to.
Why this check belongs in onboarding
Three reasons, in ascending order of cost.
Input tax. VAT charged by a business that is not validly registered is not VAT. Recovering it as input tax is not straightforward, and the exposure sits with you.
Invoice validity. A VAT invoice needs the supplier's registration number. A wrong number is a defective invoice.
Fraud patterns. Invented or hijacked VAT numbers are a standard component of missing trader fraud. The check is ten seconds. The alternative is explaining, later, why nobody performed it.
How this fits the wider registry picture
A VAT number check answers a narrow question: is this tax registration real, and whose is it.
It is not a company check. It tells you nothing about directors, ownership, accounts or solvency. For those, the UK register itself is free and unusually generous, publishing directors, persons with significant control and downloadable accounts.
The two checks are complementary and take about a minute together.
| Question | Where |
|---|---|
| Is this VAT number valid, and whose is it | HMRC VAT checker |
| Does this company exist, who runs it, who owns it | Companies House |
| What are its accounts | Companies House, free PDFs |
The summary
| You want to | Answer |
|---|---|
| Confirm a GB VAT number is valid | ✅ Free, HMRC |
| Get the registered name and address | ✅ Free |
| Prove you performed the check | ✅ Enter your own VAT number in the second field |
| Search by business name | ❌ Not possible |
| Check a GB number in VIES | ❌ Great Britain is outside VIES |
| Check an XI number | ✅ VIES |
| Sanity-check a number offline | ✅ Modulus 97 check digit |
| Check while your own registration is pending | ❌ Unavailable |
Frequently asked questions
How do I check a UK VAT number?
Use HMRC's service at gov.uk/check-uk-vat-number. It confirms whether the number is valid and returns the registered name and address of the business. It is free and needs no account.
How do I get proof that I checked a VAT number?
Enter your own VAT registration number in the second field. HMRC then records the check and gives you documented evidence of when you performed it. Leaving that field blank gives the same answer with no record.
Why does a UK VAT number fail in VIES?
Because Great Britain is outside the EU VAT Information Exchange System. GB numbers must be checked with HMRC. Only Northern Ireland numbers, which carry the XI prefix under the Windsor Framework, validate through VIES.
What is a UK VAT number format?
Usually GB followed by nine digits. Branch traders have twelve digits, the nine digit number plus a three digit branch identifier. Government departments use GD plus three digits from 000 to 499, and health authorities use HA plus three digits.
Can I check a VAT number by company name?
No. HMRC's service requires the number itself. VAT numbers usually appear on invoices, receipts or a business's website.
What is the VAT number check digit?
The last two digits of a standard nine digit number, calculated with a modulus 97 formula. You can test it offline by weighting the first seven digits by 8, 7, 6, 5, 4, 3 and 2, adding the check digits, and confirming the total is divisible by 97. Older numbers use a variant, so a failure on a very old number is not conclusive.
What if a supplier's VAT number is not valid?
Check the transcription, the format and whether you used the right system, then check whether the registration has been cancelled or is not yet live. If it still fails, raise it with the supplier before paying VAT on their invoice.
Is the VAT checker the same as a company search?
No. It confirms a tax registration and the name it belongs to. It says nothing about directors, ownership, accounts or solvency. Companies House covers those, free of charge.
Can I check my own VAT number is registered?
Yes, but not while your registration application is still being processed. The service is unavailable to you until HMRC responds.
Sources
The scope of the HMRC checking service, the information it returns and the proof-of-check function are taken from the GOV.UK service pages consulted in August 2026. VAT number formats, including branch trader, government department and health authority variants, are HMRC conventions. The modulus 97 check digit description is the published algorithm and is offered as a sanity check, not as a substitute for verification with HMRC.