The so-called “one-in, one-out” plan was signed in July and took effect in August as Prime Minister Keir Starmer’s government faced growing pressure to control record levels of immigration.

The appeal was lodged with France’s highest administrative court, the Council of State. The NGOs argue that the deal should have been ratified by parliament before it came into force.

“The implementation decree... is tainted with illegality, as it fails to comply with the procedure prescribed by the constitution,” the groups said in a joint statement.

Among the organisations involved are Utopia 56, which supports migrants, and the medical charity Médecins du Monde.

Their lawyer, Lionel Crusoe, said France’s constitution requires any such bilateral agreement to be approved by parliament before being signed into law. He said the court is expected to decide by the end of the week whether to hold a hearing.

UK deports Indian man to France under 'one in, one out' migrant scheme

Record crossings continue

Under the deal, Britain has so far removed 26 people to France and taken in 18 migrants in return, the British government said last week.

British authorities had hoped the deal would curb record levels of irregular Channel crossings, which have fuelled the rise of the hard-right Reform UK party.

The organisations argued that "the number of dangerous and illegal crossings of the Channel has not decreased" following the agreement.

More than 8,400 migrants have entered the UK on dinghies since the deal was implemented, according to an AFP count based on official British data.

Nearly 35,500 such migrants have landed on British shores since the beginning of the year.

At least 27 people have died trying to make the perilous Channel crossing by sea during that same period, according to an AFP tally of official figures.

(with newswires)