With payment initiation, settlement is part of the overall payment process and is dictated by the rules of the national settlement system(s) involved. In the UK, this is the Faster Payments system.
Faster Payments transactions are normally completed and settled within seconds during normal working hours, with cleared funds in the beneficiary bank account. Outside of working hours, settlement usually occurs within seconds, but it can take up to two hours for settlement to be completed, depending upon which pair of banks is involved in the transaction.
The Payments Services Directive states that any payments made on the Faster Payments scheme must arrive by the end of the following business day at the latest. Each bank is responsible for registering faster payments, contact your bank directly if a payment is taking an unusually long time to clear.