A French minister's warning that Paris would no longer stop migrants from crossing the Channel if Britain votes to leave the EU won a sceptical response from pro-Brexit campaigners Thursday who dismissed it as scaremongering.
In an interview with the Financial Times, French Economy Minister Emmanuel Macron said a so-called Brexit could scupper an agreement that allows Britain to conduct border controls in Calais.
"The day this relationship unravels, migrants will no longer be in Calais," he said, echoing British government warnings that a vote to leave the European Union in the June 23 referendum could result in thousands arriving on England's southern shores overnight.
Under the 2003 Le Touquet border treaty, Britain is allowed to carry out border checks on French soil, stopping many migrants.
But those pushing for Britain to leave the bloc reacted with scepticism, however, noting that it contradicted the official position of the French government.
Last month, French Interior Minister Bernard Cazeneuve dismissed the idea of ripping up the Le Touquet treaty, saying it would give a green light to people smugglers and would only boost the numbers trying to cross.
"That is the genuine line to take from the French government," Conservative lawmaker Bernard Jenkin from the Vote Leave campaign told the BBC on Thursday.
"What we are having now is propaganda being produced by other European governments at the request of the prime minister to try to scare people (out of) voting Leave."
Another group pushing for a Brexit, Leave EU, said the border treaty was a bilateral agreement that had nothing to do with Britain's membership of the European Union.
Campaign spokesman Jack Montgomery said of Macron's comments: "Absolutely nothing has changed, besides the need to scare British voters."
The question of what to do with the thousands of people camped out in Calais will take centre stage in Thursday's summit between French President Francois Hollande and British Prime Minister David Cameron in the northern French city of Amiens.
The number of those trying to reach Britain from France reached a crisis point in recent months, as a huge influx of people fleeing war and poverty in the Middle East and Africa have arrived in Europe.
French authorities on Monday began dismantling a shantytown known as the Jungle, where thousands of people live while they try their luck trying to cross the Channel, many by sneaking onto lorries boarding ferries bound for England.
Ahead of the summit, Britain agreed to contribute around 20 million euros in extra funding to boost security at Calais, on top of 60 million euros already pledged, France's minister for European affairs Harlem Desir said.
Immigration is a major issue ahead of the EU referendum, with campaigners for a Brexit warning that leaving the 28-member bloc is the only way for Britain to regain control of its borders.
Opinion polls suggest that the British public is almost evenly divided on whether to stay or leave the EU.