The bank account validation tool will let you enter a bank sort code and an account number and determine whether the account is valid for the sort code. If the sort code is valid then you will be able to see the contact details for the branch and bank it relates to.

Note: this tool does not check that an account does exist, only that the number is valid for the given sort code. You will need a pay-as-you-go licence to use this tool and 1 credit will be consumed per lookup.