The Extended Industry Sorting Code Directory (EISCD)
The EISCD is a comprehensive database of payments-related information for financial institutions participating in the UK Payment Schemes: Bacs, CHAPS, Faster Payments and Cheque and Credit Clearing. For example, sorting code 00-00-00 would represent the main bank office, and the first subbank office registered would have the suffix 01.
The checksum enables the initiator of any transaction to perform a sanity check of any specified bank account number on their own computer prior to actually initiating a request.