Curbs on foreign travel should continue in order to stop Covid variants coming to the UK, a group of MPs has said.
More details are expected this week confirming whether international travel can restart from 17 May in England.
But the all-party parliamentary group on coronavirus said restrictions should be kept in place beyond that date.
Airports are a “breeding ground” for the virus, with arrivals mixing together despite travelling from green, amber or red countries, the group said.
The group of more than 60 MPs and peers said the government should discourage people from travelling abroad unless it is essential.
It has also published a list of recommendations to make airports safer, including making sure arrival halls have enough space to social distance and separate travellers coming from higher-risk countries.
Foreign holidays are currently banned, but a traffic light system of rules is going to be introduced with countries classed as green, amber or red.
Travellers to green countries will not need to isolate on their return, but they will need to take a Covid test.
Arrivals from amber countries will need to quarantine, while red-list countries have the strictest rules, with only UK or Irish nationals allowed to return and they must pay to stay in a government quarantine hotel.
Further details are expected this week, after the government said it will “set out by early May” how countries will be categorised.
Liberal Democrat MP Layla Moran, who chairs the group of MPs that has issued the warning, said “the model we have right now has too many holes [and] is too risky”.
“It is staggering that the government is even contemplating encouraging overseas holidays when airports are already struggling to keep the virus and new variants at bay,” she said.
The group is calling for stricter checks on Covid test certificates, after the trade union representing border staff said officials spot around 100 fake Covid test certificates a day.
The European Commission has also recommended opening up to travellers who have received both doses of the vaccine.
The boss of Thomas Cook earlier told the BBC he expected many popular destinations, particularly in Europe, to be open to UK holidaymakers this summer.
“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,” said Alan French.
“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.”
Mr French also said his company had noticed many people were booking holidays as larger groups since they had not seen their families and friends in such a long time.
The first ministers of Scotland and Wales have previously argued that 17 May will be too early for foreign holidays to resume, and no date has yet been set for rules to be relaxed. Northern Ireland’s executive has not said anything about when it expects to make an announcement.
But a representative from the travel industry in Scotland has said any plan needs to be agreed between the four nations.
“There’s no way it’s going to work [with] Scotland operating a different system to England when you can freely travel across the [Scotland-England] border and fly out of an English airport – and that’s exactly what will happen,” said Alan Glen, from the Scottish Passenger Agents Association.
Mr Glen, who also runs Blantyre travel agents Glen Travel, said: “We have to have a four-nations approach to this.
The next stage of England’s lockdown easing is expected in a fortnight, on 17 May. As well as the possibility of international travel, people will be able to meet in groups of up to 30 outdoors, and six people or two households can meet indoors.
A government spokesperson said the traffic light system will allow the UK to manage the risk from different countries.
“We introduced robust border controls to stop coronavirus variants in their tracks and every essential check we’ve introduced for arrivals has strengthened our defences against new mutations.
“As the UK unlocks domestically and with many British families spread far and wide, we understand that people may need to travel abroad for all sorts of reasons.”