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.
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The outward code is the first section and enables mail to be delivered to the correct part of the country. This part contains an identifier for what area the letter should be sent to. e.g L9 identifies a delivery group in Aintree, Fazakerley, Orrell Park and Walton.
The inward code includes one number followed by two letters - and is what is used to sort the mail into the delivery office. PostcodeAddressFile.co.uk explains: "The number identifies the sector in the postal district. The letters then define one or more properties in that sector."
There are 42 unique outward postcodes in Liverpool. PostcodeAddressFile.co.uk explains how letters C, I, K, M, O, V are not used in the second part of the postcode.
The website also shared how certain letters are unable to appear next to each other to avoid confusion. It said: "The format and rules concerning postcode layout, in particular, which letters can or cannot be used, stem from the fact that certain characters or combinations of characters could be confused (e.g. ‘O’ with ‘Q’, or ‘V' with ‘W’)."
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