CH154520 | Penalties for failure to pay on time: rules for specific taxes: Stamp Duty Reserve Tax (SDRT): 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 SDRT by the penalty date, they become liable to a penalty on the amount unpaid.
The penalties for failing to pay SDRT 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 accountable date for payment - the date when the accountable person needs to pay the tax, and
the penalty date - which is the first date on which a penalty is chargeable for a tax period.
FA09/SCH56/PARA3