The Department of Transport has issued the initial list of "Travel Corridor" countries. From 10th July 2020, if you are travelling to the UK from one of these countries, and have not been in a country that is not on the list during the preceding 14 days, you do not need to self-isolate on your arrival in the UK.
The list is available here:
If you have been to or stopped in a country that’s not on the travel corridor list you will have to self-isolate until 14 days have passed since you left that country.
Arrival in the UK
Before your arrival in England, you must complete a passenger locator form. You must present these details on your arrival in England. This applies to both visitors and UK residents.
Updates to the travel corridor list
The Department of Transport will keep the conditions in these countries and territories under review.
Travellers should always check the latest FCO travel advice. Travel advice includes information on any health measures in place for visitors to the country or territory. These can include a requirement to self-isolate, quarantine, or undergo testing for coronavirus, or even restrictions on entry.