A Bacs payment is a bank transfer from one bank account to another bank account, taking three business days to arrive. However, a Bacs payment can also be a Direct Debit, which is the opposite of a bank transfer - meaning a business pulls money out of a bank account with relevant permission of the other party. Bacs payments are not same-day payments or instant, but it is still the number one bank payment type businesses use in the UK.
The alternative to slow Bacs payments are either CHAPS or Faster Payments. Both are more expensive than Bacs but take significantly less time to sent. CHAPS are same day payments for high value transfers which cost about 20-30 pounds per transfer. Faster Payments charges are much lower, and it is even faster than CHAPS, only limitation is the 250,000 pounds limit per payment.