Slightly off topic, but those here saying (and I get why) we should all wait until next year to fly abroad need to realise that all the airlines and travel companies are on their knees right now. If there isn't a reasonable trade this summer, there will be mass redundancies (& associated scrapping of aircraft/equipment) and come 2022 there will be far lower capacity available for the demand, which will push prices through the roof.
Maybe a compromise some will accept and that's fair enough, but I doubt the 100,000's in the industry will think the same!
I would imagine that when international travel resumes, the Foreign Office advice for each country will be based on the infection rate, the vaccination rate, and which variants are circulating in that country.
You are likely to see a version of the normal situation whereby:-
- The FCO advises against all travel
- The FCO advises against all but essential travel
- There is no restriction on travel
Some countries are likely to require proof of vaccination as a condition of entry, others may accept proof of vaccination or a negative COVID test, others may not impose any restrictions at all.
Whether quarantine or testing is required on return may depend on which of the above three categories each country is placed into.
However I do think that once vaccination and testings becomes widespread, an international journey would be no more risky than one within just one country. Why would London to Paris, for example, be any more risky than London to Edinburgh?