The number of migrants successfully reaching the UK after crossing the Channel has soared in recent years.
France stressed on Thursday it will not tolerate any "financial blackmail" or flouting of international law after the UK said it planned to turn back migrant boats crossing the English Channel.
French Interior Minister Gérald Darmanin wrote on Twitter that "France will not accept any practice contrary to the law of the sea, nor any financial blackmail".
"Britain's commitment must be kept," he said, adding: "The friendship between our two countries deserves better than posturing that undermines cooperation between our services."
The warning comes after Darmanin met with his British counterpart, Priti Patel, on the sidelines of a meeting of G7 interior ministers in London on Wednesday, during which Patel demanded French authorities do more to stem the flow of migrants reaching UK shores.
The number attempting to cross the English Channel in small boats has been increasing, although figures show new asylum applications in the UK are well below those in other large western European countries.
Several British news outlets reported on Thursday that British Border Force staff were to receive training on how to turn back migrant boats before they reach the coast.
Darmanin had raised concerns over such pushback tactics in a letter to Patel on Monday, which he said, "would risk having a negative impact on our cooperation".
"We call on the British government to be cautious about the announced use of operating methods to combat attempted sea crossings, which would not only be dangerous for the men, women and children on board these boats but would also be contrary to international law," he also said.
Paris and London announced in July that the UK would pay France €62.7 million in 2021-2022 to clamp down on illegal immigration via the English Channel. The money was to go towards doubling the numbers of officers patrolling the coast and increasing technology and vehicles to boost surveillance.
According to the Home Office, the cooperation between the two countries has so far prevented more than 10,000 migrants from attempting the dangerous crossing. The Joint Intelligence cell created in July 2020 has also enabled nearly 300 arrests relating to small boat criminality and the seizing of nearly 400 small boat related equipment by French authorities which have led to 65 convictions.
The French interior ministry says France has more than doubled its resources along the northern coast with 670 police officers and gendarmes, with new equipment, leading to a rise in the prevention rate from 52% last year to 62% in 2021. "It therefore rings hollow to hear that France would not be honouring its commitments," Darmanin said.
However, a recent bout of good weather has led thousands of migrants to land on beaches in southeast England, including 785 on Monday alone.
On Tuesday and Wednesday, UK authorities had to rescue or intercept a total of 757 people in the English Channel during 26 events, while French authorities intercepted 628 people in 17 separate events.
More than 14,000 have made the crossing this year, according to Britain’s Press Association news agency. In 2020, about 8,500 people made the journey, and several died in the attempt.
Dan O’Mahoney, Britain's Clandestine Channel Threat Commander, said that "this unacceptable rise in dangerous crossings is being driven by criminal gangs and a surge in illegal migration across Europe".
“But there is more to do. The Government’s New Plan for Immigration is the only credible way to fix the broken asylum system, breaking the business model of criminal gangs and welcoming people through safe and legal routes," he added.
Critics slam pushback plan
The draft bill will increase jail time for people illegally entering the country and see asylum seekers' claims rejected if they entered the UK via a "safe country" such as France. The UK group Refugee Action says there is no international legal obligation for a person to claim asylum in the first safe country they reach.
Opposition politicians and refugee groups in Britain say turning back boats in the Channel would be impractical, dangerous and illegal.
Tony Smith, a former head of Britain’s Border Force, said trying to force back overloaded and often unseaworthy boats would be “highly dangerous.”
“The top priority in my book, under the UN Convention of the Law of the Sea, is the preservation of life above all else, and so both the French and the British should be committed to that, and making sure that nobody dies,” he said.
NGOs have slammed the proposals as "inhumane". The UN's refugee agency (UNHCR) warned that it is based on a "discriminatory two-tiered system" and that it would weaken protections for asylum seekers and refugees.