XI prefix
The post-Brexit ISO code assigned to Northern Ireland VAT numbers used for goods trade with the EU under the Windsor Framework.
What it is
The XI prefix is the country code assigned to Northern Ireland for EU VAT purposes following Brexit. A Northern Irish VAT number takes the form XI followed by the same 9-digit numeric structure as a GB VAT number (e.g. XI123456789). The XI prefix routes the VAT number through VIES rather than the HMRC API, because Northern Ireland remains within the EU's VAT area for goods under the Windsor Framework.
Where you meet it
You meet the XI prefix on invoices from Northern Irish businesses that sell goods to EU customers, and on VIES lookups that return XI-prefixed results for those businesses. In vatverify, a number beginning with XI is validated against VIES, not HMRC. A number beginning with GB is validated against the HMRC VAT number API.
Goods vs services
The XI prefix applies only to goods. For services, Northern Irish businesses are treated as UK businesses and use GB-prefixed VAT numbers routed through HMRC. This creates a situation where a Northern Irish business may hold both a GB VAT number (for domestic and services transactions) and an XI VAT number (for intra-EU goods trade). Both numbers are valid for their respective contexts.
Why XI exists
When the UK left the EU in January 2021, all GB VAT numbers were removed from VIES. However, the original Northern Ireland Protocol (later replaced by the Windsor Framework in 2023) kept Northern Ireland within the EU customs union for goods to avoid a hard border with Ireland. The XI prefix was created to allow Northern Irish businesses to continue appearing in VIES for EU goods trade while the rest of the UK moved to the HMRC system.
Common confusions
- An XI number is not a GB number, even though the digits are structurally identical. Routing an XI number to HMRC will fail; it must go through VIES.
- Not every Northern Irish business holds an XI number. A business that trades only in services, or only domestically, may hold only a GB number.