A traffic light system could enable overseas travel, with countries such as South Africa and South America marked red, a Government scientific adviser has said.

Professor Andrew Hayward, from University College London and a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), suggested holidays abroad could be possible with the right structures in place.

It comes after Dr Mike Tildesley, a member of the Spi-M modelling group which advises the Government, said over the weekend that international travel this summer is “extremely unlikely” due to the risk of importing variants.

Prof Hayward told Radio 4’s Today programme: “I suspect what we may end up with is some sort of traffic light system with some countries that are no-go areas, for example likely to be South Africa and South America; other areas where there will be more severe restrictions, there will be some combination of vaccine certificates, testing and maybe quarantine, and maybe there will be some low-risk countries that you can go.”

Under the current road map for easing restrictions, the earliest date people in England could go on holiday abroad would be May 17.

A Government taskforce is considering how international travel will work and is due to report to Prime Minister Boris Johnson on April 12.

Laboratory studies have suggested that vaccines may not work as well against Covid-19 variants, particularly the South African variant.

Prof Hayward said: “If that strain starts to become dominant in this country, that would be a very bad thing.

“We can see in some areas of Europe it is starting to creep up from very low levels to 10-15-20% (of cases) in some areas, and so that’s a worrying trend.

“Increasing global travel will increase the spread of these variants. That’s our main threat in this whole strategy.”

Care minister Helen Whately said it was “premature” to consider booking a holiday abroad, telling BBC Breakfast: “I know everybody feels like it is time for a holiday, we all need that.

“It just so happens that when I was on holiday last August, I in fact booked my next holiday, which is a UK holiday, for later on in the summer.

“But my advice would be to anybody right now just to hold off on booking international travel.

“The Prime Minister launched a taskforce looking specifically at international travel that will be reporting back shortly and it just feels premature to be booking international holidays at the moment.”

Asked whether the road map target of foreign travel possibly starting up on May 17 was likely to be pushed back, Ms Whately added: “I don’t think it is helpful for me to say one way or the other.

“What I would counsel is caution at the moment for people to hold off on booking because, as anybody can see, we are in a situation where there are rising rates in many countries in Europe and we know that also something that comes with rising rates is increased rates of variants, which is why it is so important that we are going to be able to test more rapidly for variants of concern, as I have outlined.”

Tim Alderslade, chief executive of Airlines UK, said: “It is too early to say what the state of Covid will be in Europe and globally in 10 weeks’ time.

“Our focus between now and then must be working with ministers on a framework for travel that is robust and workable, and can stand the test of time as we enter the all-important summer period.

“We have always said any reopening must be risk-based, but also led by the overriding assumption that as the vaccine rollout accelerates both here and abroad, a phased easing of restrictions is achievable.

“We know that universal, restriction-free travel is unlikely from May 17 but under a tiered system, based on risk, international travel can meaningfully restart and build up, with minimal restrictions in time.”

Paul Charles, chief executive of travel consultancy The PC Agency, which introduced an unofficial traffic light system last summer, said: “Widespread testing on arrival at the airport, as well as the introduction of a clear traffic light system, would enable safe and responsible overseas travel to resume, while also protecting two million jobs at risk if travel this summer can’t be saved.

Consumers are prepared to accept sun, sand, sea and swab tests this summer if it means a safe overseas trip

“The traffic lights system would bring much-needed clarity to consumers as countries would be categorised by criteria including the status of their vaccine rollout, infection rates and hospital infrastructure.

“It would be designed to give visibility to those going away on how a country is performing and what the risks may be.

“The system could be updated each week, in line with the EU’s own system, and if consumers are forced to return from their trip early due to a higher risk emerging, then it could be done with less distress than was caused last summer by the sudden removal of travel corridors.

“Consumers are prepared to accept sun, sand, sea and swab tests this summer if it means a safe overseas trip.”

Regarding the UK, Prof Hayward said relaxing restrictions to allow outdoor socialising in April was “a move that will improve a lot of people’s lives”.

He said outdoor transmission of the virus is much less likely than indoor transmission, and that also applied to being outdoors at bars and restaurants.

Asked if the UK could live with a greater amount of transmission of the virus going forward, he said: “I think the vaccination programme has been extremely successful which does give us… quite a lot more leeway in that respect.

“But we still at the moment have over half a million over 65-year-olds unvaccinated and two and a half million over 55-year-olds unvaccinated, so if we let things go then there’s a lot of people who could still get very ill.”

He said vaccine uptake was much lower in places such as London and Manchester and so we “may see sort of pockets of a rising infection that lead to hospitalisations and deaths”.

He added: “We are keeping an eye on cases but we’re also being particularly careful to see how those are translating into hospitalisations and deaths.”