The UK is wide open and no active protocols seem to be in place. The behavior of the vast majority of people indicates that in their minds the pandemic is over. You can count on the fact that the person sitting two rows away from you on the plane or tube and coughing repeatedly is not wearing a mask and his/her mother never taught about the proper way to cover a cough.
It can be tough if you are a protocol follower/ masker like myself to keep from feeling a little upset. That test to return home lingers in the back of your mind. However, it is important to remember the population is following what the government has asked them to do, which is basically nothing.
Part of challenge of travel during Covid times is being willing to accept the practices of the country you are in. The requirements may be stricter or looser than what you are used to, but acceptance is the key.