The British government plans to warn holidaymakers against visiting popular tourist destinations such as Spain because of concerns about the COVID-19 pandemic, the Times reported on Monday.
Such a step could trigger an exodus of about a million British tourists already abroad, cause further damage to the travel sector and deal a new blow to southern Europe's summer tourist season.
The Times did not specify what particular concerns Britain had about Spain. Madrid has been hit by the more infectious Delta coronavirus variant, but its rolling seven-day infection rate dropped throughout last week.
Britain has double vaccinated a higher proportion of its population against COVID-19 than most other countries, but the government has prevented travel to many countries by imposing rules that the travel industry says is hobbling the economy.
A spokesperson for Britain's transport ministry declined to comment on The Times report, published on the day when rules were eased for double-vaccinated travellers from the United States and most of Europe.
Prime Minister Boris Johnson's travel rules have angered some of Britain's European allies, frustrated millions of sun-seeking Britons and brought warnings from airports, airlines and tour companies.
In a letter to Johnson that was leaked to media, finance minister Rishi Sunak called for an urgent easing of travel restrictions.
Under rules to be reviewed on Thursday, double-vaccinated travellers can return without quarantining from countries rated "amber" on a "traffic-light" list assessing the COVID-19 risk.
Those returning from red-list countries - the most severe risk - must pay 1,750 pounds to spend 10 days in a hotel.
An amber watchlist was due to be signed off on Thursday but a split in the government could delay a decision, The Times said.
Spain would be put on the new list under the plans, the Times said. It is unclear what the plans are for two other popular tourist destinations, Greece and Italy.
Citing the threat posed by the Beta coronavirus variant, England has maintained quarantine rules for double-vaccinated travellers from France, while scrapping the requirement for travellers from other medium-risk "amber" countries.
France has complained, saying the bulk of its Beta variant cases come from the island of La Reunion in the Indian Ocean.