For those taxpayers required to submit a 2020 Self assessment Tax Return (normally self-employed/higher incomes/complex affairs) the deadline for filing is as normal on 31 January 2021.
Last year the Govt allowed people to delay their advance payment due on 31 Jul 2020 by 6mths. This ends on 31 January, and it isn’t being extended, You need to speak to HMRC if you are unable pay by this date and you may be able to agree a separate repayment plan.