Peppol ID Northern Ireland: GB or XI VAT number?

There is no XI scheme in Peppol. A VAT-registered Northern Ireland business would normally register a Peppol ID under scheme 9932 (United Kingdom VAT number), the same as a business in Great Britain, for example 9932:gb123456789 (a made-up number). The XI prefix is a separate VAT matter. It affects what you print as your VAT number on certain invoices, not your Peppol address.

Two different things: your address and your VAT number

On a Peppol invoice, your identity appears in two separate places:

Element	Business term	Purpose	NI example
cbc:EndpointID	BT-34 Seller electronic address	Routing: where the invoice is delivered over Peppol	schemeID="9932" GB123456789
cac:PartyTaxScheme/cbc:CompanyID	BT-31 Seller VAT identifier	Tax data shown on the invoice	GB123456789 or XI123456789

The electronic address must match a Peppol ID registered in an SMP. Otherwise nobody can deliver to it. The VAT identifier is invoice content, and it follows VAT rules.

So an NI business can keep a single Peppol ID and still show an XI VAT number on the invoices that need one.

When the XI prefix applies

HMRC's manual on Northern Ireland and the EU says businesses trading goods between Northern Ireland and the EU need, "where appropriate", to add "the 'XI' prefix before their normal 9-digit UK VAT number" when communicating with EU suppliers or customers.

The same page says the XI prefix is not required:

• for services between Northern Ireland and the EU
• within the internal UK market
• for goods or services between the UK and the rest of the world

GOV.UK's registration guidance adds: "You must use your XI VAT registration number on all documentation when communicating with EU customers or suppliers", including invoices. You start using it once HMRC confirms you are eligible.

In practice, then:

Invoice	VAT identifier (BT-31)	Peppol ID (EndpointID)
NI supplier to GB customer (goods or services)	GB123456789	9932:gb123456789
NI supplier to NI customer	GB123456789	9932:gb123456789
NI supplier of goods to an EU customer	XI123456789	9932:gb123456789
NI supplier of services to an EU customer	GB123456789	9932:gb123456789

This table reflects HMRC's general XI guidance. It is not tax advice, so check HMRC's guidance for your own transactions.

Can you register 9932:xi123456789?

Technically, the Peppol identifier policy allows any value made of letters, digits and a few symbols, and the 9932 entry has no validation rule. So nothing in the Peppol rules stops a provider registering 9932:xi123456789. But:

• 9932 is defined as "United Kingdom VAT number", and its listed country is GB.
• Your customers' systems will most likely look you up under the GB form.
• When we searched the Peppol Directory on 20 October 2026, Northern Ireland registrations we found used the 9932:gb... form.

Registering an XI-based Peppol ID as well as, or instead of, the GB one is likely to cause missed lookups. Unless a buyer specifically asks for it, the GB form is the safer choice.

Does the validation accept XI?

Yes. EN 16931 rule BR-CO-09 requires the seller and buyer VAT identifiers to start with an ISO 3166-1 alpha-2 country prefix ("Nevertheless, Greece may use the prefix 'EL'"). The EN 16931 UBL validation artefacts used by Peppol BIS Billing 3.0 include XI in their list of accepted prefixes. So XI123456789 in BT-31 will pass that rule.

The postal address country is a separate question. GB is the official ISO 3166-1 code for the whole United Kingdom, including Northern Ireland. But the country code list published with Peppol BIS Billing 3.0 also contains XI, "United Kingdom (Northern Ireland)", so an address with country XI will also validate. No UK rule yet says which one NI businesses should use, so ask your provider what it does.

Worked example

Lough Components Ltd (fictional) in Belfast has UK VAT number 123 4567 89 and has been confirmed to use XI for EU goods trade.

• Peppol ID: 9932:gb123456789, registered once by its provider.
• Invoice to a customer in Manchester: BT-31 GB123456789. Buyer's EndpointID is the customer's Peppol ID.
• Invoice for goods to a customer in Dublin: BT-31 XI123456789. Same seller EndpointID. Buyer's EndpointID is the Irish customer's Peppol ID, which may use an Irish scheme.

What is not settled for the UK mandate

Confirmed: Peppol will be the core interoperability network for UK e-invoicing, with mandatory e-invoicing for B2B and B2G VAT invoices from April 2029.

Not yet confirmed (as of 20 October 2026):

• whether UK rules will say which scheme and value format NI businesses must register under
• whether any UK-specific validation will check that BT-31 uses GB or XI correctly for the type of supply
• whether NI postal addresses should use country code GB or XI
• how the mandate will interact with EU e-invoicing rules for NI goods trade with EU member states

See E-invoicing in Northern Ireland and XI VAT numbers for the wider picture.

What to do now

1. Keep one Peppol ID based on your GB VAT number unless a customer asks otherwise.
2. Make sure your invoicing software can switch BT-31 between GB and XI by type of supply, not by customer alone.
3. Ask your provider how it validates VAT prefixes.
4. Related reading: Peppol participant IDs in the UK and EAS codes 9932 and 0088.