It's interesting that the UK is an outlier. I checked a couple of weeks ago, and there were 130+ countries with travel restrictions in place on entrants. The UK seems to have no such restrictions, you can fly into LHR from pretty much anywhere (COVID-19 hotspots included), and from what I've heard there isn't a great deal of testing being done on arrivals at LHR.
Mind you, this is a country which still tells its citizens that wearing masks is inadvisable. Apparently, requiring that people wear masks - even of the basic paper or cloth mask kind that are totally unsuitable as PPE for medical staff - would suddenly threaten the totemic NHS with PPE shortages. This is not an issue anywhere else in Mainland Europe, because governments apparently realise that the kind of basic masks that ordinary citizens wear aren't displacing the supply of much higher standard masks used by healthcare workers.