Campaigners for Brexit have poured cold water on suggestions that The Jungle migrant camp in Calais could be moved across the Channel if the UK votes to leave the European Union.
French finance minister Emmanuel Macron indicated that a Leave vote on June 23 could result in Paris tearing up a treaty which allows UK border officials to carry out checks on the French side of the Channel.
Speaking ahead of talks between David Cameron and French President Francois Hollande in Amiens, Mr Macron told the Financial Times: "The day this relationship unravels, migrants will no longer be in Calais."
Mr Macron also suggested that France would "roll out the red carpet" for bankers fleeing the City of London for the continent following Brexit, and cautioned that any country leaving the 28-nation bloc would not retain the same access to the single market.
In an echo of Mr Cameron's 2012 offer to welcome businessmen fleeing high-tax France, Mr Macron told the FT: "If I were to reason like those who roll out red carpets, I would say we might have some repatriations from the City of London."
During the two-year process of negotiating a new relationship with a departing member, the EU's "collective energy would be spent on unwinding existing links, not recreating new ones", he said.
Mr Macron's comments were dismissed as "scaremongering" by London mayor and leading advocate of Brexit Boris Johnson.
Breaking into Franglais during a visit to south London, Mr Johnson told the Press Association: "I would say 'Donnez-moi un break'. There's absolutely no reason why that treaty should be changed.
"It was an inter-governmental treaty, it was the Le Touquet treaty. It was signed between the British government and the French government. It's not in the French interests to want to do that and it's just the usual flapping and scaremongering."
Meanwhile, Cabinet minister Chris Grayling, who is also campaigning for Leave, pointed to recent comments by French interior minister Bernard Cazeneuve, who said that dropping the border co-operation with Britain would be "foolhardy".
In the House of Commons, Conservative MP Peter Bone asked Mr Grayling about Mr Macron's suggestion that 4,000 inhabitants of The Jungle would be "put in rubber boats and come across to Britain" - something which he said the French should be "ashamed" about.
The Leader of the Commons responded: "Of course I have heard in the last couple of weeks the French interior minister reassure us that the bilateral agreement that exists between the United Kingdom and France over border controls is one that the French government would not wish to put at risk."