More countries could be struck off the quarantine exemption list amid fears over a second wave of coronavirus in Europe.
Destinations with soaring infection rates like Belgium and Luxembourg could join Spain with returning holidaymakers needing to self-isolate for 14 days.
Ministers are also said to be “keeping an eye” on Croatia, a popular spot for British tourists, after a surge in cases.
It would mean more disruption for thousands of Brits planning foreign holidays in those countries – and prompt fears that France and Germany could follow.
Cabinet minister Oliver Dowden said he understood public “anxiety and frustration” with the measures but the Government had to try to avoid a second wave in the UK.
He claimed there was “no viable alternative” to the quarantine policy – while testing passengers at airports was not a “silver bullet”.
And Heathrow Airport boss, John Holland-Kaye, said the UK “needs a passenger testing regime fast”.
Ministers will meet Thursday to discuss the quarantine rules and announce any changes on Friday.
But they are still advising Brits to book summer holidays abroad despite fears over coronavirus spikes across the continent.
Mr Dowden said holidaymakers could go ahead with plans but “need to be aware of the risk that quarantine could be imposed”.
The top Tory added: “But as long as people are aware of that risk they should continue to book holidays, but just bear in mind that this may happen, and it has happened in Spain.”
The advice is in stark contrast to Scottish First Minister Nicola Sturgeon who suggested she would not book a foreign holiday this summer.
At least 11 countries where quarantine-free travel is possible have recorded increases in cases in recent days, with some reaching higher infection rates than Britain.
Belgium’s rate of new confirmed cases has gone from 6.2 per 100,000 population a fortnight ago, to 12 last week, to 19 this week, according to the latest weekly figures from the European Centre for Disease Prevention and Control.
France’s rate has gone from 5.7 to 8.7 over the same period while Germany has increased from 2.9 to 4.6 per 100,000.
Spain, which is now on the quarantine list, went from 8.9 a fortnight ago, to 18.9 last week, up to 29.7 this week.
A report by the London School of Hygiene and Tropical Medicine said that quarantining people for eight days on arrival from the EU and testing them on day seven, with a 24-hour turnaround in results, could reduce the number of infections by 94%.
Mr Holland-Kaye said the Government needed to introduce an “alternative to the cliff-edge” of quarantine for free travel and said a testing system could be “up and running within a couple of weeks”.
France is currently testing a similar approach.
But Mr Dowden said: “We are not at the point where there is a viable alternative to the 14-day quarantine. There is a real risk here – the virus is spreading around the world rapidly.
“We need to ensure that the measures we’ve taken in the UK – which have been very difficult – to keep this virus under control, do not go to waste because we allow cases to come in from elsewhere.”
Covid-19 cases in Britain have risen with the average number of infections jumping by 14% in a week. However, scientists urged ministers not to panic as rises were expected as lockdown eased.
The Department of Health announced that 763 people tested positive for the virus, up from 697 yesterday and 638 last Wednesday.
The World Health Organisation’s Europe director warned that young people could be driving the spikes in infection across the continent.