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 will grant asylum to one migrant in France who can prove a family connection to the U.K. in exchange for each arriving migrant taken back by 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”.