France could end British border controls in Calais and allow thousands of refugees to cross the Channel in the event of a Brexit, a minister has said.

Emmanuel Macron, the French finance minister, told the Financial Times that a "leave" vote in June's EU referendum may stop “Le Touquet” agreement, which allows British immigration checkpoints in Calais and Dunkirk and French checks in Dover.

“The day this relationship unravels, migrants will no longer be in Calais,” he said.

Demolition of France's 'Jungle camp' continues

Current regulations mean that entry to the UK can be refused before entering the Channel Tunnel or boarding ferries, rather than once passengers exit on British soil the other side.

It enables lorries to be searched and scanned for stowaways, with any migrants found arrested or removed from the area by police and drivers fined.

Moving the Border Force checks to the UK could mean that refugees would be the other side of the Channel before being discovered, giving them the right to apply for asylum and stay in the country until a decision is made.

Around 4,000 migrants and refugees are currently living in a camp known as the “Jungle” in Calais, with more in Dunkirk, all trying to reach England.

In pictures: Calais crisis Show all 15 1 /15 In pictures: Calais crisis In pictures: Calais crisis Calais crisis Migrants climb in the back of a lorry on the A16 highway leading to the Eurotunnel in Calais Getty Images In pictures: Calais crisis Calais crisis Protesting French employees of the company English Channel passenger and freight ferry company "MyFerryLink" block the railway tracks of the Eurostar Channel tunnel line in Calais Getty Images In pictures: Calais crisis Calais crisis Protesting French employees of the company English Channel passenger and freight ferry company "MyFerryLink" block the railway tracks of the Eurostar Channel tunnel line with a burning plastic barrier In pictures: Calais crisis Calais crisis French riot police officers drive out protesting French employees of the freight ferry company MyFerryLink Getty Images In pictures: Calais crisis Calais crisis French riot police take position to drive out protesters blocking the railway tracks Getty Images In pictures: Calais crisis Calais crisis Passengers stranded by the cancellation of Eurostar trains wait at St. Pancras station in London. Eurostar said it has canceled all passenger trains through the tunnel that links France and England, after striking ferry workers swarmed the train line setting tires alight In pictures: Calais crisis Calais crisis Passengers sit on stairs after being stranded by cancelled Eurostar trains at St. Pancras station in London In pictures: Calais crisis Calais crisis A police vehicle drives past lorries are backed up on the M20 motorway which leads from London to the Channel Tunnel terminal at Ashford and the Ferry Terminal at Dover In pictures: Calais crisis Calais crisis Trucks queue up as part of Operation Stack in Dover In pictures: Calais crisis Calais crisis Cars queue to board a ferry in Dover bound for Dunkirk, France, as the disruption at Calais looks set to enter a second day as migrants continue to target lorries in a bid to cross into the UK In pictures: Calais crisis Calais crisis A police officer sprays tear gas to migrants trying to access the Channel Tunnel on the A16 highway in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Migrants wait near the A16 highway as they try to access the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Striking employees of the French company My Ferry Link, a cross-channel ferry service, stand in front of tyres set on fire as they block the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis A striking employee of the French company My Ferry Link, a cross-channel ferry service, sits on a tyre in front of tyres set on fire as he takes part in a blockade of the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images In pictures: Calais crisis Calais crisis Striking employees of the French company My Ferry Link, a cross-channel ferry service, prepare to set tyres on fire to block the access to the Channel Tunnel in Calais, northern France PHILIPPE HUGUEN/AFP/Getty Images

French authorities are gradually demolishing hundreds of tents and shacks, claiming they have sufficient accommodation to rehome migrants in other areas of the country, but activists claim they have underestimated numbers and will leave thousands without shelter and even more desperate to leave.

David Cameron was accused of “scaremongering” when he claimed that a Brexit could see the camps move to Britain last month.

The Vote Leave campaign group said Downing Street’s warning that the French would “love to pull out” of the 2003 treaty had “no grounding in reality”, while Eurosceptic Tory MP David Davis branded the prospect “preposterous”.

At the time, the French interior ministry pointed to a statement by interior minister Bernard Cazeneuve saying there were "no plans" to change the agreement, which was drawn up as part of a bilateral treaty.

Migrants watch a hut burn as police officers clear part of the 'jungle' migrant camp on February 29, 2016 in Calais, France (Getty Images)

Sir Peter Ricketts, the former UK ambassador to France and national security advisor, warned that the French government was under pressure from opposition parties to scrap it.

“If the context changed and Britain made a major decision to leave the EU I think it’s highly likely France would review its position too," he told BBC Radio 4.

Downing Street said the Prime Minister and François Hollande were expected to discuss the situation in Calais at the Anglo-French summit today.

Mr Cameron is expected to make a joint announcement with French President in Amiens on security and other benefits of remaining within the EU.