Travellers returning from the Greek islands of Lesbos, Tinos, Serifos, Santorini and Zakynthos will no longer need to self-isolate.
The relaxed measures will apply to people arriving in England, Wales and Northern Ireland - but Scotland is yet to confirm whether it will follow suit.
It follows a drop in new coronavirus infections in the popular tourist destinations, and will come into effect at 4am on Saturday.
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However, Transport Secretary Grant Shapps has said no countries are going to be removed from England's quarantine list this week.
Rory Boland, travel editor of Which?, said it came after "yet another week of intense speculation about which countries will be removed from the travel corridor list".
"This approach is confusing and costly, with speculation that their destination may be added to the quarantine list causing some travellers to needlessly cancel their trip, therefore losing their right to a refund," he said.