SolvedCH153640 | 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 - further penalties
From HM Revenue & Customs · Compliance Handbook
If any amount remains unpaid 5 months after the penalty date, the person is liable to a 5 month further penalty of 5%, as well as any initial penalty that they have already incurred.
If any amount remains unpaid 11 months after the penalty date, the person is liable to an 11 month further penalty of 5%, as well as any initial penalty or 5 month further penalty that they have already incurred.
See the example at CH153680.