Today HMRC has announced that Self Assessment customers will not receive a penalty for filing their 2019-20 tax return late, as long as they file online by 28 February. Tax-payers who have not filed yet are still being encouraged to do so by 31 January, if possible.
You still need to pay your Self Assessment tax bill by 31 January and interest will be charged from 1 February on any outstanding liabilities. Full details of how to pay may be found on the .gov website here: https://www.gov.uk/pay-self-assessment-tax-bill
If any tax-payer cannot afford to pay by 31 January, they may be able to set up an affordable plan and pay in monthly instalments. But they will need to file their 2019-20 tax return before setting up a time to pay arrangement.