The United Kingdom formats its IBANs in 22 characters, and it is one of the few countries whose BBAN opens with letters: the pattern is ^[A-Z]{4}[0-9]{14}$. Those four letters are the bank identifier, normally matching the first four characters of the institution’s BIC.
Anatomy of a GB IBAN
Take the official registry example, GB29 NWBK 6016 1331 9268 19 (a published SWIFT registry test value, not a live account):
GB- country code29- IBAN check digitsNWBK- 4-letter bank code (here derived from NatWest’s BIC)601613- the 6-digit sort code, the same number UK customers use domestically31926819- the 8-digit account number
Nothing is hidden or transformed: the sort code and account number appear in the IBAN exactly as they are used for domestic Faster Payments, BACS and CHAPS. That is unusual - France, for instance, appends a clé RIB, and Hungary embeds extra check digits.
Domestic format and its quirks
UK domestic banking predates the IBAN by decades and still runs primarily on the sort code plus account number pair. Some UK account numbers are historically shorter than 8 digits; banks zero-pad them for IBAN purposes, but the padding convention can vary by institution, so always prefer the IBAN printed on a bank statement over one you assembled yourself. The UK BBAN itself carries no separate national check digit; integrity relies on the two ISO 7064 MOD-97 check digits at positions 3-4, plus the industry’s own modulus checking of sort code and account number combinations, which happens inside bank systems rather than in the IBAN.
SEPA status and verification
The UK participates in SEPA despite not being an EU member, so euro payments to a GB IBAN route through the normal SEPA rails. Keep in mind that a checksum-valid GB IBAN says nothing about whether the account is open or who owns it. UK banks address the ownership question with Confirmation of Payee, the domestic equivalent of the EU’s Verification of Payee, which compares the recipient name you enter against the bank’s records before money moves.