CH154100 | Penalties for Failure to Pay on Time: Rules for specific taxes: Registered Pension Scheme (RPS): Penalties: Failure to pay all or part of amounts due - overview
From HM Revenue & Customs · Compliance Handbook
If a person fails to make a full payment of income tax under the Registered Pension Scheme (RPS) by the penalty date, they become liable to a penalty on the amount unpaid.
The penalties for failing to pay income tax under the RPS in full and on time are
So a failure to pay that continues for 11 months after the penalty date can incur all of these penalties on the same unpaid tax.
It is important to distinguish between
the due date - the date when the person needs to pay the tax, and
the penalty date - which is 31 days after the due date and the first date on which a penalty is chargeable for a tax period.
There are special rules for the penalty dates relating to assessments in absence of a return, corrections and amendments, see CH154200.