The UK transport minister says the beta variant has been a concern not just in French overseas territories but also in parts of mainland France.
Britain has defended its decision to maintain quarantine requirements for fully vaccinated travellers from France after Paris slammed it as "discriminatory" and "incomprehensible."
"The big concern is that we don't allow a variant in which somehow is able to escape the vaccine programme that we have got," UK Transport Secretary Grant Shapps told Sky News.
British authorities waived on Wednesday their 10-day self-isolation requirement for travellers from amber countries — which include the US and European Union member states — as long as they are fully vaccinated against COVID-19 with jabs authorised by the EU and US regulators.
But the measure, which comes into force on August 2, does not include France, which the UK has classed as "amber plus", citing the Beta variant as a concern.
The French say the beta variant is not prevalent in mainland France but in some of the country's overseas territories.
"If I understood correctly, it is in the name of the Beta variant, the infamous variant from South Africa, which represents less than 5% of the cases in France and mostly in the overseas territories which are not concerned by the (travel) flows towards the United Kingdom," France's Europe Minister, Clement Beaune told French broadcaster LCI on Thursday morning.
"This is scientifically unfounded. It is a discriminatory decision, I think, towards the French, because all Europeans, even from countries with more difficult health situations than ours — because of the Delta variant or else — are not concerned, or no longer concerned, by the quarantine," he said.
"It is excessive and frankly incomprehensible from a health point of view."
But Shapps said on Friday that the virus strain was also an issue in northern France.
"The Beta variant, it is not just - as has been reported - on an island thousands of miles away, it was also an issue in particular in northern France. So it has been an overall concern," Shapps said.
The UK is in France's "orange" category, meaning that fully vaccinated people can travel to France without submitting to quarantine upon arrival.
Both France and the UK recorded over 27,000 new infections on Wednesday but over the course of the past week, the UK recorded 71,000 more new cases than its neighbour across the Channel. During the previous seven-day period, the UK had recorded over 333,000 cases to France's 81,877.
France remains behind on vaccination but is catching up after a slow start. It has so far administered at least one dose of the vaccine to 73% of its adult population and fully inoculated 62% of people aged 18 and over.
In the UK, more than 88% of adults have received at least one dose and 71.1% is fully vaccinated.
Transport Minister Grant Shapps said the quarantine decision for France would be reviewed "at the end of next week."
"We say to the British, on the scientific level, on the health level, there is no justification for this decision and therefore I hope that it will be reviewed, it is common sense, as soon as possible," Beaune said.
Reached by Euronews, the UK's Department for Transport did not directly address the criticism but indicated that it was "working to extend our approach to other vaccinated passengers in the future".
Britain's decision to create an "amber plus" category for France in mid-July had already drawn criticism, notably from the sizeable French community in the country who bemoaned that an easing of self-isolation rules for amber countries did not apply to them and their families on the other side of the English Channel.
"This pandemic and the constant travel rule changes have had a huge impact on the French community in the UK that, along with industry-leading companies from the travel and tourism sectors, fail to understand this last-minute decision from the UK Government," Olivier Boudard, who launched a petition calling for France to be treated as an amber country, wrote.
His petition has gathered more than 6,300 signatures in a week.
Another petition launched since the latest announcement urges the government to allow fully-vaccinated people from France without quarantine, arguing: "This is separating families."