You also will not get reliable information until closer to your travel and by posting the specific routing.
Some countries have instituted border controls with passport checks and others have not. That is bound to change between now and January 1, not to mention thereafter.
My recommendation, given the fluidity of the pandemic as well as the disharmony associated with Brexit is that you use the time between now and 31 December to renew your passport so that yours becomes an academic question.
To be clear, whatever happens, you won't be denied entry to the UK, presuming that your location is your citizenship as well.