[This was originally posted prematurely in incomplete form. Sorry.]
The BBC website has an article, dated June 19, with potentially encouraging news for folks hoping to visit the UK from some countries in Europe. It's a bit vague, and the degree to which individual statements are related is not totally clear to me, but I think this is a fair summary; I encourage everyone to read it for themselves. I don't want to quote big chunks due to copyright limitations.
The UK is planning to relax the quarantine requirements for some countries in early July. It is talking to Portugal, France, Italy, Greece and Spain. There may be a June 29 announcement on "travel corridors", meaning that people travelling between the countries would not have to self-isolate. The effective date might be as early as July 4.
People arriving from other destinations will still be required to quarantine, and a senior aviation source said that requirement could continue through the summer for visitors from countries not part of one of the UK travel corridors.