Britons could face added travel restrictions with several countries thought to be considering tough new regulations on UK visitors.
France may impose strict new rules and Italy and Spain are also looking closely at new rules as part of attempts to counter a rise in the omicron variant.
French officials have suggested UK visitors could be forced to take PCR tests on arrival, adding extra costs to a Christmas trip.
There are also fears over a growing wave of infections in Spain and Italy with cases also reported in the Netherlands and Czech Republic as the outbreak spreads across mainland Europe.
Gabriel Attal, a spokesman for the French government, said: "Regarding Britain, the current rule is to show a negative test less than 48 hours old in order to enter France. But we are always looking at means to tighten the framework. We are currently working on that and we should, I think, come to a conclusion in the coming days.”
It is expected that France will mirror the testing requirements of the UK for French visitors.
This would mean UK visitors to France would have to complete a PCR or lateral flow test within 48 hours of departure for France, followed by a PCR test on arrival - which would add substantial extra costs for a family break. It is likely it would cover anyone aged over 12.
There were also indications on Tuesday that Italy is preparing to toughen its restrictions, with anyone unvaccinated arriving in the country required to quarantine for five days and undergo Covid tests.
Meanwhile, Eurostar has said the rate of new bookings has more than halved since tougher testing requirements for travellers were introduced.
The cross-Channel rail operator said that for the Christmas and New Year period, more passengers were cancelling or rearranging planned trips than booking new ones.
Jacques Damas, chief executive of Eurostar, said: "We understand and support the need for governments to take actions against Covid-19 to protect public health.
“However, as the Government itself confirmed last week, the omicron variant is likely to be dominant in the UK very soon, which makes additional restrictions on travel rather redundant. It comes at a heavy price for the industry and brings an unwelcome additional cost for passengers at an expensive time of year."
He added: "We therefore ask governments to urgently remove the additional testing which is unfairly impacting the travel industry and our passengers who seek to reunite with friends and family over the Christmas period."
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