People will be able to go on holidays “within limits” this summer, a leading expert has claimed, while ministers said the travel green list will be coming soon.

However, Peter Openshaw, Professor of Experimental Medicine at Imperial College London, said it was vital people do not drop their guard because there are likely to be further outbreaks of coronavirus.

Prof Openshaw, who is also a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nertag), told the Andrew Marr Show on Sunday the UK needed to be cautious and prepare.

When asked if people will be able to start going on holiday, he said: “Yes, within limits.

“It’s so important that we do not drop our guard completely.

“We know it’s perfectly likely there will be further outbreaks unless we use this time to be very cautious and prepare sensibly.”

His comments come as Foreign Secretary Dominic Raab said the list of nations where international travel will be permitted is “coming shortly”.

He told The Andrew Marr Show: “We said we’d make the changes on May 17 and we would set out the details of the new system, which is a traffic light system, before then. So, it’s coming shortly.”

The ban on foreign holidays is expected to be lifted for people in England from May 17 as part of the next easing of coronavirus restrictions.

The traffic light system will be risk-based, with different rules for people returning to England depending on which list their destination is on.

Many people are eager to discover what countries are on the green list to avoid the need to self-isolate.

The Department for Transport missed a deadline set by a committee of MPs for grading countries under the new traffic light system for international travel.

The Commons’ Transport Select Committee issued a report which stated the green, amber and red lists of destinations must be published by Saturday “at the latest”, but this has not happened.

Instead, the Department for Transport (DfT) has only said the lists will be made public in “early May”.

Earlier in the week, Transport Secretary Grant Shapps said holidaymakers in England will be able to use the NHS app to prove their coronavirus status to destination countries.

Mr Shapps said the app – which is currently used to book medical appointments and order repeat prescriptions – will display evidence that someone has been vaccinated or recently tested.

He told Sky News: “In terms of vaccine certification, I can confirm we are working on an NHS application; actually it will be the NHS app that is used for people when they book appointments with the NHS and so on, to be able to show you’ve had a vaccine or you’ve had testing.

“I’m working internationally with partners across the world to make sure that system can be internationally recognised, as that’s the way forward.”

The European Union has previously set out plans for coronavirus vaccine certificates that could be used by UK holidaymakers this summer.

Digital green certificates will be accepted as evidence that a person has had a Covid-19 jab, received a negative test result or recovered from the virus, according to the European Commission’s proposal.

Spain’s tourism minister, Fernando Valdes Verelst, told an international summit held by the World Travel & Tourism Council in Mexico that the country will welcome back tourists – including those from the UK – in June.