LONDON/PARIS - Britain has approved plans to turn away boats illegally carrying migrants to its shores, deepening a rift with France over how to deal with a surge of people risking their lives by trying to cross the Channel in small dinghies.

Hundreds of small boats have attempted the journey from France to England this year, across one of the world's busiest shipping lanes. The summer surge happens every year, but is now larger than normal as alternative routes have been shut down.

Border officials will be trained to force boats away from British waters but will deploy the new tactic only when they deem it safe, a British government official who asked not to be named said on Thursday.

Michael Ellis, Britain's acting attorney-general, will draw up a legal basis for border officials to deploy the new strategy, the official said.

Home Secretary Priti Patel told French Interior Minister Gerald Darmanin that stopping people making their way from France on small boats was her "number one priority".

Patel had already irritated the French government earlier this week when she indicated Britain could withhold about 54 million pounds ($75 million) in funding it had pledged to help stem the flow of migrants.

Darmanin said Britain must honour both maritime law and commitments made to France, which include financial payments to help fund French maritime border patrols.

"France will not accept any practice that goes against maritime law, nor financial blackmail," the French minister tweeted.

In a letter leaked to British media, Darmanin said forcing boats back towards the French coast would be dangerous and that "safeguarding human lives at sea takes priority over considerations of nationality, status and migratory policy".

Britain's Home Office, or interior ministry, said: "We do not routinely comment on maritime operational activity."

POLITICALLY CHARGED

Charities said the plans could be illegal and some British politicians described the idea as unworkable.

Channel Rescue, a citizen patrol group that looks for migrants arriving along the English coast, said international maritime law stipulated that ships have a clear duty to assist those in distress.

Clare Mosely, founder of the Care4Calais charity, which helps migrants, said the plan would put the lives of migrants at risk. "They're not going to want to be sent back. They absolutely could try and jump overboard," she said.

Tim Loughton, a member of parliament for the ruling Conservatives, said the tactics would never be used because people would "inevitably" drown.

"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 drowning," he said.

A spokesman for Prime Minister Boris Johnson said the government was exploring a range of safe and legal options to stop the boats.

The number of migrants crossing the Channel in small dinghies has risen this year after the British and French governments clamped down on other forms of illegal entry such as hiding in the back of trucks crossing from ports in France.

The numbers trying to reach Britain in small boats - about 13,000 so far in 2021 - are tiny compared with migrant flows into countries such as Lebanon and Turkey, which host millions of refugees.

But the issue has become a rallying cry for politicians from Johnson's Conservative Party. Immigration was a central issue in the referendum decision in 2016 to leave the European Union.

France and Britain agreed in July to deploy more police and invest in detection technology to stop Channel crossings. French police have confiscated more dinghies but they say they cannot completely prevent departures. 

British junior health minister Helen Whately said the government's focus was still on discouraging migrants from attempting the journey, rather than turning them back.

Britain's opposition Labour Party criticised the new approach as putting lives at risk and it said the priority should be to tackle people-smuggling gangs. ($1 = 0.7241 pounds)

(Reporting by Andrew MacAskill and Richard Lough Editing by William Schomberg, Timothy Heritage, William Maclean) ((Andrew.MacAskill@thomsonreuters.com; +447818584430; Reuters Messaging: andrew.macaskill@thomsonreuters.com))