Bacs is the company which runs both the direct debit and direct credit scheme in the UK.
There are rules governing these schemes and the latest version can be found by going to www.bacs.co.uk/documentlibrary
The Bacs scheme rules will evolve over time. It is the service users responsibility to ensure the latest version of the rules are being applied. If as a service user you are unsure how to comply with these rules then please speak to your sponsoring bank.