The Royal Mail has explained two letters can never appear next to each other in a UK postcode.
The mail service created the postcode system to maintain a database of deliverable addresses. The combination of letters and numbers is an abbreviated form of an address that identifies a location where something needs to be delivered to.
The codes were first introduced in Norwich in 1959 with every address in the UK now falling under a postcode. Postcodes are split into two sections with the outward followed by the inward code.
