Finland, Switzerland, the Azores, Liechtenstein and Lithuania are also on the "green list" as of 04:00 BST.
Travellers from newly red-listed Thailand and Montenegro now need to isolate in government-approved hotels.
All arrivals must take at least one Covid test - but many countries have banned UK residents from entering.
Travellers coming from green list countries do not need to quarantine when they come back to the UK - whether or not they have had two doses of a coronavirus vaccine.
They still have to be tested before their return to the UK, however, and book a test for day two after their return, and fill in a passenger location form.
Only British or Irish nationals and UK residents are allowed into the country if they have been to red list countries. They then have to pay to self-isolate in a government-approved quarantine hotel.
Most countries are on the amber list - fully-vaccinated adults do not have to quarantine on their return from these locations, but do have to have tests before returning and two days after they get back.
Those who have not had both vaccines have to isolate at home for 10 days, as well as having Covid tests.
The travel industry has criticised the UK's changing travel rules, with airlines saying the system risked making international travel "more expensive, burdensome and uncertain compared to other countries".
Travel lists are currently updated every three weeks and the system is similar for England, Scotland, Wales and Northern Ireland.
* Countries are placed on different coloured lists depending on the Covid situation in each nation
* Green list countries are said to carry the lowest risk for travellers - and so isolation is not required, though testing pre-arrival and on day two is needed
* Most countries - including the UK's most popular holiday destinations - are on the amber list
* Amber list arrivals do not need to isolate if they are fully vaccinated or under-18 - but testing is required pre-arrival and on day two after landing
* Those who have yet to have both jabs will need to isolate and take additional Covid tests
* Only British nationals can enter the UK directly from a red list country and they must pay to quarantine in special hotels and be tested