The British home secretary, Priti Patel, has been accused by France’s interior minister of plotting “financial blackmail” and a violation of international maritime law in a deepening diplomatic row over efforts to prevent migrants from crossing the Channel by boat.
Gérald Darmanin said that UK plans, released on Wednesday night, to send back boats of vulnerable people into French waters would not be accepted by his government.
“France will not accept any practice that breaks maritime law, nor any financial blackmail,” Darmanin wrote on Twitter. “Britain’s commitments must be respected. I said this clearly to my counterpart” during a meeting on Wednesday, he added.
The statement from Darmanin, Patel’s counterpart, reflects anger in Paris about reported plans by the British government to begin turning back boats carrying migrants once they enter UK waters in the Channel.
Patel, who is under pressure from Boris Johnson and Tory MPs to halt the Channel crossings, has approved the new hardline strategy.
She is widely considered to be one of three cabinet ministers vulnerable to a demotion in an expected reshuffle by the prime minister.
French officials have also been angered by suggestions that Britain could withhold some of the €62.7m (£55m) it promised earlier this year to fund policing and patrols in northern France unless more is done to prevent migrant crossings.
A French interior ministry source said there had “never been any question of making payment conditional on numerical targets”.
“Such an approach would reflect a serious loss of confidence in our cooperation,” the source said.
In a further development, the UN’s special rapporteur on migrant rights, Felipe González Morales, said that UK plans would prevent the right to seek asylum, and affect children.
“Very worrisome measure that could amount to ‘pushbacks’, preventing the exercise of the right to seek asylum and other internationallly recognized human rights, affecting also children,” he wrote on Twitter.
The plans, which were briefed to government-friendly media on Wednesday night, are already “dead in the water”, an immigration workers’ union has said.
Lucy Moreton, a professional officer at the Immigration Services Union said she would be surprised if the policy, unexpectedly announced as criticism of the government’s social care reforms was mounting, was used “even once”.
“There are understandably a lot of constraints around it and you cannot do this with a vessel that is in any way vulnerable and more importantly you need the consent of the French to do it.”
Tim Loughton, a Conservative MP and member of the home affairs select committee, also poured cold water on the prospects of the tactic being used in practice, although he supported the underlying principle.
He said: “It sounds good. But I’m afraid in practice it’s just not going to happen. These are flimsy boats coming over. Even those that are tougher are completely weighed down.
“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 … and then we’ll get blamed for that. It sounds good pushing them back but it’s not going to work in practice.”
A Home Office source said the plans were one part of planned reform to the immigration system and had been fully examined by the government. “We are looking at this as one part of reform of the entire system. We believe there would be a deterrent effect from making the journey in the first place,” the source said.