HM Treasury has issued a new Treasury Direction

See link:

Some key points:

  1. The scheme has been extended to 30 April 2021;
  2. It clarifies that furlough pay in March/April 2021 should reference pay in March/April 2019, and not March/April 2020, due to the fact that some employees may have been on furlough pay);
  3. The calculation for ‘usual hours’ of work is similarly amended.
  4. The deadline for amending a claim is extended from 15th of the following month to the end of the following month.