SolvedCH64250 | Penalties for Failure to File on Time: How to process a penalty: Amendment of penalties
From HM Revenue & Customs · Compliance Handbook
We can assess a tax-geared penalty for a failure to file even if the person has not yet filed the return. In that case, we calculate the penalty as a percentage of the liability to tax that we expect to be shown in the return in question, see CH63560.
If we have done this, we will amend the penalty when the failure is finally remedied and the tax liability is known.
We cannot amend the penalty percentage that was used in the original calculation unless there is evidence of a more serious behaviour attracting a higher level of penalty.