A "one in, one out" deal agreed by the UK and French governments on Thursday proposes that for each migrant the UK returns, Britain will accept another who has made a legal claim in France.

Britain’s migrant return deal with France is “robust” against legal challenge, Downing Street said as the EU suggested it is assessing whether the agreement complies with “the spirit and letter of the law”.

The U.K. agreed in 2022 to pay France some $650 million over three years to help turn back migrants who gather on the French side to cross. Thousands of migrants wait in makeshift camps in and around the port city of Calais in Northern France to attempt the perilous journey.