If you reside in America and fly to the UK or Ireland you have 14-day quarantine in a hotel at your own expense.

If you are an American you cannot fly to any of the EU nations nor to Iceland, Norway, Switzerland and Liechtenstein. There are exemptions for "health workers, seasonal farm workers, diplomats, humanitarian workers, transit passengers, asylum seekers, students and “passengers traveling for imperative family reasons"".

So if you want to pick leeks, strawberries or other crops and live with Romanians and Bulgarians you can go.

Or if you are an American and live in Algeria, Australia, Canada, Georgia, Japan, Montenegro, Morocco, New Zealand, Rwanda, Serbia, South Korea, Thailand, Tunisia and Uruguay and have a residency card from that nation you can fly into the EU.