UK Sort Code + Account Numbers _do_ have check digits (Its not precisely a check digit as such: they have rules that they have to obey to be valid). Because of the age of the system, there isn't one _consistent_ rule for all sort code and account numbers, but instead a document listing the various methods and a couple of tables saying which rule(s) to apply and how

In most cases the sort code is included in the checksum

https://www.vocalink.com/media/3513/vocalink-validating-acco...