If the UK votes to leave the European Union border controls at Calais could be dropped, allowing migrants to stream across the English Channel, France's economy minister Emmanuel Macron has warned.
He said that if the UK votes for Brexit, France could drop the Le Touquet agreement it has with the UK that allows the UK to carry out border controls on the French side of the Channel.
"The day this relationship unravels, migrants will no longer be in Calais and the financial passport would work less well," Macron told the Financial Times.
The announcement is a blow to Out campaigners, who have previously said Brexit wouldn't lead to an ending of the bilateral agreement, as the deal is simply one between the UK and France.
Yet Leave campaign group Leave.EU hit back, saying: "Just last month, the French government reiterated its sensible position that 'calling for the border with the English to be opened is not a responsible solution.'"
"'It would send a signal to people-smugglers and would lead migrants to flow to Calais in far greater numbers', the interior minister said. 'A humanitarian disaster would ensue. It is a foolhardy path, and one France will not pursue'. Absolutely nothing has changed, besides the need to scare British voters," Leave.EU said.
French authorities earlier this week began dismantling part of the so-called Calais Jungle, relocating migrants to nearby shipping containers.
Speaking ahead of the Anglo-French summit, Macron also said that he expected financial services workers in London to relocate to Europe, as their firms will have effectively lost the "passport" rights that allow them to operate across the EU.
"The day this relationship unravels, migrants will no longer be in Calais and the financial passport would work less well," Macron added.
He also said that Britain would lose full access to the single market if left the EU. “People deciding to leave the single market will not be able to secure the same terms.”