SolvedCH153620 | Penalties for Failure to Pay on Time: Rules for specific taxes: Bank Payroll Tax (BPT): Penalties: Failure to pay all or part of amounts due - initial penalty
From HM Revenue & Customs · Compliance Handbook
A person incurs an initial penalty when they do not pay the BPT by the due date. They become liable to the penalty on the penalty date.
The amount of the initial penalty is 5% of the amount unpaid at the penalty date.
See the example at CH153680.