CH63540 | Penalties for Failure to File on Time: Calculating the penalty: Calculation process: Calculating fixed and daily penalties
From HM Revenue & Customs · Compliance Handbook
A person is liable to fixed penalties, and daily penalties for certain taxes, when they fail to file their return by the filing date.
Fixed penalties
A person becomes liable to an initial fixed penalty of £100 when their return is not filed by the filing date for both
In addition to incurring the initial fixed penalty,
Fixed penalties are a fixed amount and are not based on the tax liability of the return.
Daily penalties
For occasional returns and returns for periods of 6 months or more, see CH62120, daily penalties of £10 per day can be charged after 3 months from the penalty date. Although £10 is charged each day, the total of the daily charges make up one penalty. The final daily penalties charge is for the lesser of
the number of days from when the daily penalties first start being charged up to and including the date on which the return is filed, and
90 days.