As you will be aware HMRC had maintained that they would not offer an extension to the filling deadline for self assessments. They had decided to issue penalty notices for late filling, as they normally would, but offer leniency if the return was not filed due to pandemic related disruption. However, HMRC have now stated that any return filed before the 28 February will not attract a penalty notice.
Taxpayers are still obliged to pay their bill by the 31 January and interest will be charged from 1 February on any outstanding liabilities. If a client cannot afford to pay their bill on time they can apply to spread their bill over a period up to 12 months, but they will need to file their 2019-20 tax return to do this.