Experts have warned that overseas summer holidays for Brits are looking "unlikely" amid surging virus numbers in Europe and fears of variants.
Government scientist Dr Mike Tildesley said that the UK faces a "real risk" if people travel abroad, while travel secretary Grant Shapps said it was "too early to tell" when foreign travel might be back on.
"I think we are running a real risk if we do start to have lots of people going overseas in July, for instance, and August because of the potential for bringing more of these new variants back into the country," Tildesley said.
"What is really dangerous is if we jeopardise our vaccination campaign by having these variants, where the vaccines don't work as effectively, spreading more rapidly."
The warnings come as travel companies mark out plans and recommendations for the summer months. The boss of Australian airline Quantas told the BBC this weekend that governments would "insist" on vaccines for international travel and that many were talking about it as a "condition of entry."
"We have a duty of care to our passengers and to our crew, to say that everybody in that aircraft needs to be safe," said chief executive Alan Joyce.
"The vast majority of our customers think this is a great idea — 90% of people that we've surveyed think it should be a requirement for people to be vaccinated to travel internationally."
UK holiday bookings surged following prime minister Boris Johnson's announcement of a roadmap out of lockdown a month ago.
Under the current UK roadmap, the earliest date people in England could plan to go abroad would be 17 May.
On Friday, airline association IATA called for a specific roadmap for travel around the world to follow the UK's example. Director general Alexandre de Juniac said that vaccination certificates were "not a silver bullet" and expressed concern about the continuing lack of coordination between governments.
At the end of February, EasyJet said flight bookings from the UK jumped 337% and package holiday bookings surged 630% compared with a week earlier, with Málaga, Alicante and Palma in Spain, Faro in Portugal and the Greek island of Crete among the top destinations. August breaks are the most popular, followed by July and September.
Watch: EU Plans Digital Vaccine Passports to Save Summer Holidays