frankv:mudguard:
IE to prevent someone depositing money in the wrong account because they got a digit wrong in the account number.
There are some checks... I believe that there's a checksum on the digits. So in theory getting a single digit wrong would be picked up. But getting two digits wrong, or transposing 2 digits could through.
The account numbers have a check digit in them, typically a mod-11 but it used to vary a bit by bank, which will detect single-digit errors and most transpositions, doubling-up errors, and the like.