The mass reopening of international travel could “screw up” the UK’s recovery from coronavirus and must be delayed until other countries match Britain’s vaccination programme, according to the transport secretary.

Grant Shapps said that the government had to be “cautious” over foreign holidays because of the risk of importing more cases of the Indian strain of Covid-19.

He denied claims that the government was close to placing more countries on the green list, which allows Britons to travel abroad without quarantining on their return.

He said the government was “having to wait for countries to catch up” with the vaccination programme before the list was expanded. In the UK, 75 per cent of adults and about 60 per cent of the population have had one dose of a vaccine compared with about 40 per cent of the population of many European countries such as Spain, France, Portugal and Greece.

“What no one wants to see us doing now is to screw that all up by inadvertently re-attracting the coronavirus . . . into this country,” Shapps told Sky News.

There has been criticism from airlines and tourism groups over the refusal to expand the 11-strong green list, which largely comprises countries that are effectively out of bounds to UK travellers. This week, Portugal was removed from the list even though only six out of 100,000 British tourists passing through Faro airport in the Algarve had tested positive for the virus. The UK also refused to add Malta to the green list even though it registered zero cases for the first time in almost a year this week.

Michael O’Leary, chief executive of Ryanair, described the government’s handling of foreign travel as a “shambles” and insisted there was effectively “no green list”.

“This stop, go, stop approach to travel is bonkers,” he told Sky News today . “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.”

Forecasts drawn up by the Airport Operators Association suggested 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.

The association said that UK airports lost £2.6 billion of revenue between April and September 2020, with a similar loss expected this year.

Karen Dee, its chief executive, said: “Unless the government makes a meaningful restart of aviation possible by extending the green list at the next review, moving to rapid and affordable tests for returning travellers and following the examples of the EU and the US by reducing restrictions on fully vaccinated passengers, aviation is in for an extremely difficult summer.”

The traffic light system was announced last month, allowing people to travel to green countries without quarantining on their return. Up to ten days’ isolation and two PCR tests are needed for amber and red countries.

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 is already a fear that the end of restrictions due on June 21 will be delayed by a fortnight because of the spread of the Indian or Delta variant.

Speaking from Cornwall, Shapps 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.”