SolvedCH157200 | Penalties for Failure to Pay on Time: Penalty assessments: When you must tell the person
From HM Revenue & Customs · Compliance Handbook
The appropriate time to issue the penalty assessment will depend on the individual circumstances. It should however be issued at the earliest appropriate opportunity and on or before the later of either
the end of a 2 year period beginning with the day before the penalty date, or
the end of a 12 month period that begins with either
the end of the appeal period for the assessment of the outstanding tax, or
where there is no assessment, the date when the liability was established.
The appeal period means either
the period in which the appeal can be brought, or
the period between the appeal being brought and when it is either determined or withdrawn.