Britain is threatening to harden its position on immigration and turn back small migrant boats crossing the English Channel, according to U.K. media reports, but France says such a policy would be dangerous and illegal.

A British Border Force team is being trained to employ turnaround tactics that force boats back into French waters, the BBC reported, citing an unidentified official. It was unclear if the intention is to take migrants all the way back to French shores.

Britain would only push boats back in “very certain, narrow circumstances,” the official said. Home Secretary Priti Patel might need to personally approve each case.

The news came as Patel met with her French counterpart, Gérald Darmanin, in London on Wednesday.

“I made clear that delivering results and stopping crossings were an absolute priority for the British people,” Patel wrote on Twitter afterward.

The French interior minister objected strongly. “Safeguarding human lives at sea takes priority over considerations of nationality, status and migratory policy, out of strict respect for the international maritime law governing search and rescue at sea,” he wrote in a letter to Patel released publicly after the meeting.

He followed that with a more blunt response on Thursday. “France will not accept any practice that violates maritime law, nor any financial blackmail,” Darmanin tweeted. “The friendship between our two countries deserves better than posturing that undermines cooperation.”

Patel has also stoked French anger by indicating that Britain might withhold some of the $74 million it pledged in July to help increase border patrols on the beaches of Northern France and deploy more surveillance technology in the Channel.

The British Home Office declined to comment on-the-record about the turnaround tactics, although it said it was working on “safe and legal” means to deter migrant boats from crossing the Channel.

Patel, who is charged with delivering two of British Prime Minister Boris Johnson’s key electoral pledges — controlling immigration and recruiting 20,000 extra police officers — is under increasing pressure from fellow Conservative Party lawmakers over the crossings. The Times of London on Wednesday reported that complaints from other parliamentarians could lead to her demotion.

But she has also developed a reputation for tough pronouncements on immigration that aren’t actually implemented. And on Thursday, some British politicians — including members of the Conservative Party — said the plan to turn boats back was unworkable.

“It sounds good pushing them back, but it’s not going to work in practice,” Tim Loughton, a Conservative lawmaker, told the BBC.

“Any boat coming up alongside at speed would capsize most of these boats anyway and then we’re looking at people getting into trouble in the water and inevitably, I fear, drowning … and then, of course, we will get blamed for that,” he said.

Calais, France, remains a congregation point for migrants hoping to cross the English Channel, more than four years after French authorities demolished a sprawling migrant camp there that had become a squalid symbol of Europe’s failure to manage waves of migration. The migrants included people fleeing war-torn areas and seeking refuge on European shores.

An increasing number of have tried to cross the Channel to Britain by small boat and raft, defying warnings of the dangers of undertaking such a journey in one of the busiest maritime areas in the world. Last month, a migrant died after being pulled unconscious from the water.

A record 828 migrants crossed the Channel in a single day in August. This year, 13,500 migrants have crossed the Channel in small boats, more than in the whole of 2020.

Between Sunday night and Wednesday, the French Maritime Prefecture in charge of the Channel said it undertook 11 rescue operations involving 198 “castaways.” The likely migrants were dropped off at the nearby fishing port of Boulogne-sur-Mer, where they were taken care of by rescue services personnel and border police officers.

Read more: