Home secretary Amber Rudd has further backed current British border checks in Calais, as a French minister who warned Brexit would see the deal "threatened" looks set to enter the presidential race.
Rudd visited Paris today in her first foreign trip as home secretary, and issued a joint statement with her opposite number, interior minister Bernard Cazeneuve, with both sides reiterating support for the Le Touquet deal, which allows British border checks in France.
“Effective UK/France cooperation remains crucial in addressing the shared threat we face from terrorism and extremism, as well as addressing the current challenges posed by the migratory flows to Europe,” the pair said.
“We pledge that this cooperation must and will be developed, now and after the United Kingdom leaves the EU.”
The Le Touquet deal has also been backed by French president Francois Hollande.
However, today also saw the resignation of his economic minister Emmanuel Macron - who previously warned a Brexit vote would threaten the agreement - sparking speculation he would join candidates competing to replace Hollande.
Speaking to the Financial Times in March, Macron said: "If British voters chose to exit the EU, collective energy would be spent unwinding existing links, not creating new ones. It’s not scaremongering. We have to explain how those ties would be unpicked.
"The day this relationship unravels, migrants will no longer be in Calais and the financial passport will work less well. Our will is not to revise the Le Touquet accord but it would be threatened by such a context."
Macron has yet to confirm a presidential bid, but doing so would see him join the raft of candidates who have expressed doubts on the future of the agreement.
Most recently, Hollande's predecessor Nicolas Sarkozy said this weekend the border should move to England.
Sarkozy will be among the candidates fighting the French election next May, alongside fellow Les Republicains candidate Alain Juppe, and Front National leader Marine Le Pen. All three have called for the current system to be scrapped.