The legislation that expires on 02/02/2021 says:
"Review
14.—(1) The Secretary of State must review—
(a) whether each area that is part of the Tier 2 area or of the Tier 3 area should continue to be part of that area at least once every 14 days, with the first review to be carried out by 16th December 2020;
(b) the need for each of the Tier 1, Tier 2 and Tier 3 restrictions at least once every 28 days, with the first review to be carried out by 30th December 2020.
(2) In carrying out a review under paragraph (1)(a) the Secretary of State must in particular consider whether it is necessary for each area that is part of the Tier 2 area or of the Tier 3 area to continue to be part of that area for the purposes of preventing, protecting against, controlling or
providing a public health response to the incidence or spread of infection in England with
coronavirus.
(3) In carrying out a review under paragraph (1)(b) the Secretary of State must in particular consider whether each of the restrictions continues to be necessary for the purposes of preventing, protecting against, controlling or providing a public health response to the incidence or spread of infection in England with coronavirus."
So, there must be a review by 16th December latest, but the government is able to choose to review sooner.