Portugal has been removed from the UK’s green list, as the government updated its international travel guidance.
Grant Shapps confirmed on Thursday that the popular holiday destination would be moved to the amber list from 4am on Tuesday morning.
The transport secretary said the decision was made to “make sure that we can do a domestic unlock”.
No other countries have been added to the green list.
In a broadcast interview, Shapps said: “I want to be straight with people, it’s actually a difficult decision to make, but in the end we’ve seen two things really which caused concern.
“One is the positivity rate has nearly doubled since the last review in Portugal and the other is there’s a sort of Nepal mutation of the so-called Indian variant which has been detected.
“We just don’t know the potential for that to be vaccine-defeating mutation and simply don’t want to take the risk as we come up to June 21 and the review of the fourth stage of the unlock.”
He added: ”“Europe is probably 10 weeks behind but they will catch up and I don’t know exactly what that will mean in terms of the summer but the decisive action today is designed to protect the future, to make sure that we can do a domestic unlock or give ourselves the best possible chance of doing so and that will also help us to unlock international travel given time.”
It comes amid fears the importation of new variants of Covid could derail Boris Johnson’s plans to end England’s lockdown at the end of next month.
Countries are categorised as red, amber or green, with different Covid quarantine and testing requirements.
People returning from green destinations do not need to quarantine, but those arriving from amber locations must self-isolate at home for 10 days.
Arrivals from red list countries must enter a government-approved quarantine hotel.
The decision is a huge blow for the travel industry, as Portugal was the only viable major tourist destination on the green list when it was announced last month.
It is only 17 days since non-essential leisure travel has been permitted from Britain.
Its seven-day rate of coronavirus cases per 100,000 people stands at 37.2, up from 30.7 a week earlier.