The “really concerning” Beta coronavirus variant that led to further restrictions against travelling from France has now been detected in 132 countries, the World Health Organization has said.
The strain, which vaccines may be less effective against, was why England placed France on a special amber-plus list that required travellers to quarantine for up to 10 days.
England has maintained quarantine rules for double-vaccinated travellers from France, while scrapping the requirement for travellers from other medium-risk "amber" countries.
Education minister Gillian Keegan told ITV News: "When we say we're concerned about the rise of new variants, the one we're really concerned about at the moment is the Beta variant – we've been looking at that one and that's why [France was] put on a special list."
Watch: Boris Johnson defends UK's approach to travel amid concerns
The government is also worried about the prevalence of the Beta variant in Spain.
The Times newspaper reported the UK planned to warn holidaymakers against visiting the popular tourist destination.
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.
Under rules to be reviewed on Thursday, double-vaccinated travellers can return without quarantining from countries rated "amber", under a "traffic-light" list system assessing the COVID-19 risk.
Those returning from red-list countries – the most severe risk – must pay £1,750 ($2,436) to spend 10 days in a hotel.
The WHO revealed that the Alpha variant was still the most prevalent, having been detected in 182 countries, while the Beta strain had been reported in 132 nations, Delta in 135 and Gamma in 81.
But the Beta variant – first detected in South Africa – is particularly concerning to the UK due to evidence it can escape the immune response better than others and that vaccines may therefore be less effective against it.
The UK is also concerned that a large number of Britons travelling to France and Spain during the peak tourist months may bring it back with them.
When France was placed on the amber-plus list, Sage’s Professor John Edmunds told BBC Radio 4's Today programme said: “The Beta variant has remained a threat throughout.
"It is probably less infectious than the Delta variant that is spreading here in the UK at the moment. Where it has an advantage is that it is able to escape the immune response to a better extent.”
He added: “As the population here becomes more and more immune, the conditions are right then for the Beta variant to get an advantage, so I can understand the concern.
“Of the variants that are out there and are known about, that one has always been a threat to us.
"There is some good evidence from South Africa that it can evade the immune response generated by the AstraZeneca vaccine more efficiently.”
Meanwhile, France has complained about extra travel restrictions, saying the bulk of its Beta variant cases come from the island of La Reunion in the Indian Ocean.
Watch: How the world could be better after COVID