The restart of international travel could “screw up” the UK’s recovery from the pandemic, transport secretary Grant Shapps warned.
The mass reopening must be delayed until other countries match the UK’s vaccination programme, according to the transport secretary.
The government had to be “cautious” over foreign holidays because of the risk of importing more cases of the Indian strain of Covid-19.
Shapps denied that the government was close to placing more countries on the green list, which allows Britons to travel abroad without quarantine on their return.
The government was “having to wait for countries to catch up” with the vaccination programme before the list was expanded.
Ministers came under fire from the travel industry for abruptly removing Portugal from the green list with just four days notice for travellers to return home, leaving few options for quarantine-free travel.
Three quarters of UK adults and about 60% of the population have had one dose of a vaccine compared with about 40% of the population of many European countries such as Spain, France, Portugal and Greece.
Shapps told Sky News: “What no one wants to see us doing now is to screw that all up by inadvertently re-attracting the coronavirus . . . into this country.”
Speaking from Cornwall ahead of the G7 Summit, he said: “I think most people agree that we’ve got to be cautious. I am the transport secretary, I want transport to happen, I want international transport to happen, but I think most people appreciate that what we need to do is open up cautiously.
“I hope and I am sure that will happen as more and more people are vaccinated around the world.
“Of course, what happened was that the UK got well ahead of the game in terms of more people vaccinated than any other country in Europe and so we are just having to wait for countries to catch up.”
Ryanair Group chief executive said: “This stop, go, stop approach to travel is bonkers.”
He told Sky News: “Portugal has exactly the same Covid case rates and higher vaccination rates when it was taken off the green list than it had when it went on it. Malta has higher vaccination rates than the UK.
“The whole thing is typical of Boris Johnson’s government just making this stuff up as they go along.”
The Airport Operators Association has warned that the next three months could be “as bad or worse than summer 2020” for passenger numbers.
The number of destinations people from the UK could visit last summer without needing to quarantine on their return was “significantly more” than under the present traffic light system, it said. The list is due to be reviewed on June 21.
Travel industry sources told The Times there were concerns that further changes will be delayed until mid-to-late July because of the risk posed to the lifting of domestic lockdown restrictions.
There are already doubts that the end of Covid restrictions due on June 21 will be delayed by two weeks due to the spread of the Indian or Delta variant.