Royal Mail is the authoritative organisation which owns and assigns all postcodes in the UK for the purposes of delivering mail. To check your officially assigned postcode or if you have a query, then please visit the Royal Mail website.
FindMyAddress is underpinned by Ordnance Surveys AddressBase® Premium product which comprises local authority address data along with Royal Mail postcode data (PAF®). It also assigns postcodes to physical features and objects that don’t receive mail such as open spaces and telephone boxes which is why you will see these with a postcode.
For further information, please see Ordnance Surveys AddressBase® range of products.