British holidaymakers are expected to be freed to travel to Europe's top holiday destinations next month after Brussels opened the door to vaccinated travellers from the start of June.
Spain, Greece and France are among countries that could be added to the safe "green list" by the end of June under the traffic light system being drawn up by Downing Street for international travel, The Telegraph can disclose.
On Monday, Boris Johnson played down hopes of an immediate mass getaway, saying that putting a significant number of countries on the "green list" from May 17 would risk an "influx of disease".
The Prime Minister was immediately accused of an "overly cautious" approach by Tory MPs and travel industry chiefs after the European Commission proposed that fully vaccinated Britons could travel freely to Europe without any testing or quarantine requirements from as early as the start of June.
Mr Johnson is expected this week to sign off on a "green list" comprising only a "tiny handful" of fewer than 10 highly vaccinated countries, such as Gibraltar, Malta, Israel and Iceland, which Britons will be able to visit from May 17 without having to quarantine on their return. Most of the rest of Europe will be on an "amber list", requiring quarantine.
However, a government source said the three-weekly review of the "green list" would mean more countries, potentially including some of the most popular European holiday destinations, would be added to the list through June.
"It's a rolling, evolving list that is going to start off cautiously but could start to change quickly. It is not like a one-off list that affects the totality of the summer. It will update and other countries will be added," he said.
Internal EU figures show Germany, France, Italy, Spain and the Netherlands will be in a position to fully inoculate more than 55 per cent of their populations by the end of June.
It came as the UK recorded only a single coronavirus death in a day for the first time since August last year and Mr Johnson said there was a "good chance" that the one-metre plus rule for social distancing could be ditched from June 21.
Speaking during a campaign trip to Hartlepool, Mr Johnson said: "We do want to do some opening up on May 17 but I don't think that the people of this country want to see an influx of disease from anywhere else.
"I certainly don't – and we have got to be very, very tough, and we have got to be as cautious as we can, whilst we continue to open up."
It means that changing traffic light designations of popular destinations is likely to turn 2021 into the year of last-minute booking.
The European Commission's plan, to be discussed with European nations on Tuesday and Wednesday, aims to open borders for tourism for Britons, Americans, Israelis and others from countries with low Covid and high vaccination rates in time for the summer season in June.
"One very important question linked with vaccination was whether or not individuals being vaccinated would actually break, or help break, transmission. And, fortunately, now, we do have enough solid, deep scientific evidence proving that this is the case," an EU official said.
The commission said national governments across Europe should ease "current restrictions on non-essential travel into the EU to take into account the progress of vaccination campaigns and developments in the epidemiological situation".
However, it indicated that it expected "reciprocal" treatment of vaccinated EU citizens visiting the UK, which would mean Britain easing its requirement for everyone to take a PCR test on arrival even if inoculated.
Senior Tory MPs and travel industry chiefs urged Mr Johnson to accelerate the UK. reopening. Henry Smith, the Tory chairman of the all party Future of Aviation group, said the timetable was "overly cautious".
"We risk being at a competitive disadvantage with other countries who are looking to safely open up to people who are vaccinated," he said.
“We should be pursuing routes with other countries that have similar vaccination rates, like the US. Unless we use the advantage of our successful vaccination policy, then the economy competitively will be at a disadvantage. It's not just holiday travels, it's the economic imperative."
Huw Merriman, the Conservative chairman of the all-party transport committee, said: "How can it be right that countries with slower vaccination rollouts are safely reopening to international travellers while the UK stays static?
"The Government is in danger of squandering the opportunity to take advantage of the UK's world-leading vaccine dividend as countries across the globe begin to open up for international travel."
Tim Alderslade, the chief executive of Airlines UK, said: "It is frustrating the UK has not gone down the same road as the EU, with ministers here still reluctant to acknowledge we can be more ambitious with our own plans, taking advantage of one of the most impressive vaccination programmes in the world, alongside quicker, cheaper testing and our globally renowned genomic sequencing capability."
Government officials are preparing for fewer than 10 "green list" countries when data from the joint biosecurity centre is analysed on Wednesday. Portugal and the US are the only major candidates.
The travel industry, however, still expects most EU countries to be open by the end of June. Alan French, the chief executive of Thomas Cook, said: "When the holidays proper start at the end of June, we are expecting most of the countries that the UK goes on holiday to – Europe particularly – to be open.
"We are expecting Portugal, Spain, Greece, Croatia and so forth to be open. It would be nice if Turkey was open. When we look at what is going on in those countries, both in terms of infection rates and how they are preparing for holidaymakers, I think there is great progress being made."
Fifty major UK and US travel companies and organisations, including all the major UK airports and hospitality groups, wrote to Mr Johnson and Joe Biden, the US president, urging them to announce the reopening of a US-UK travel corridor in time for the G7 summit in early June.
"It is the success [of the UK and US vaccination programmes] that now marks a significant opportunity for the UK and US to lead the world by demonstrating how to re-open this crucial air corridor safely," they wrote.