Guides · Updated 10 October 2026

Northern Ireland XI numbers: VAT and EORI

Why Northern Ireland businesses have XI numbers, when to use the XI or the GB number, and how each is checked.

Why Northern Ireland is different

When the UK left the EU, Northern Ireland stayed aligned with the EU's rules for goods, so that goods could keep crossing the border with Ireland without checks. This arrangement, first the Northern Ireland Protocol and now the Windsor Framework, means a Northern Ireland business is treated as if it were in the EU for goods, and as part of the UK for everything else.

To tell the two apart, HMRC gives Northern Ireland businesses numbers with the XI prefix for their EU goods trade.

XI VAT numbers

An XI VAT number is the business's normal UK VAT number with XI in front instead of GB: XI123456789 rather than GB123456789. It's the same registration, written two ways.

• Use the XI number for goods sold to or bought from EU businesses: it goes on the invoice and supports zero-rating, just like an EU VAT number.
• Use the GB number for services, and for goods traded within the UK or with countries outside the EU.

XI VAT numbers are in VIES, so you check them the same way as any EU number. GB numbers aren't: they're checked with HMRC's Check a UK VAT number service.

XI EORI numbers

A business moving goods into or out of Northern Ireland, for example to make a customs declaration there, needs an XI EORI number as well as its GB one. It's issued by HMRC and normally matches the GB EORI number with XI in place of GB, for example XI123456789000. The business needs a GB EORI number first.

XI EORI numbers are checked in the European Commission's EORI service, like EU ones, while GB EORI numbers are checked with HMRC. Validitool's EORI checker sends each to the right place. More in EORI numbers explained.

Common mistakes

• Putting the GB number on an invoice for goods sent to an EU customer. The EU customer can't check it in VIES, and you lose the evidence for zero-rating.
• Assuming every UK business has an XI number. Only those registered in Northern Ireland, or trading goods through it, use one.
• Treating an "invalid" GB result in VIES as a sign the business isn't registered. VIES no longer holds GB numbers at all.

This guide is general information, not tax or legal advice. Rules and their application differ by country and by transaction; check with an adviser for your situation.

More guides

• How to check an EU VAT number before you invoice
• VIES is down: what it means and what to do
• The reverse charge explained: EU and UK B2B sales
• How often should you re-check a customer’s VAT number?
• What proof of a VAT number check should you keep?
• EORI numbers explained: EU, GB and XI
• Checking Swiss and Norwegian VAT numbers
• Sanctions screening for small businesses
• Fake invoices and changed bank details: how to spot supplier fraud
• Peppol e-invoicing: what it is and how to check a customer