There isn't a single "least used postcode" in Britain, as postcodes don't have usage statistics in that way; instead, postcodes are used to define geographic areas for mail delivery, and many smaller, or newly designated, postcodes could have very low usage. However, a search for "least used postcode in Britain" is more likely to turn up information about generic postcodes (like those starting with ZZ or ending with ZZZ), which are used in specific databases for data analysis and are not associated with physical locations or actual usage.
