Also, sort codes for Northern Ireland branches of banks registered in both Northern Ireland and the Republic, are valid, and recognized for use in the Republic. These errors will be trapped by the computer program as they will result in an incorrect format.
A sort code is the name given by both the British and Irish banking industry to the bank codes which are used to route money transfers between banks within their respective countries via their respective clearance organisations. It identifies both the bank, and the branch where the account is held.