Migrants could set up camp in Folkestone and Dover if Britain decides to vote for a Brexit, David Cameron looks set to warn.

The Prime Minister is expected to claim an exit from the EU would leave the country vulnerable to terror attacks and that migrant camps would spring up across the South East.

He is thought to be making national security issues the centrepiece of his campaign to keep Britain in the European Union.

Mr Cameron will address the treaty drawn up in 2003 which allowed Britain to conduct border controls in France, rather than in the UK.

Folkestone and Hythe MP Damian Collins denied the PM was scaremongering. He said:

“It is a credible claim because the current arrangements do work massively in our favour. If the French authorities were to remove border controls, then the migrants at Calais would end up in Kent and claim asylum here...it is a real risk.”

Ashford MP Damian Green echoed: “The Prime Minister is quite right to warn about this. And it is not just the Prime Minister but the French Interior Minister who has said there is a chance of this happening and the Mayor of Calais is actively campaigning to end the treaty.”

But Ukip leader Nigel Farage dismissed the claims, pointing out that the treaty which had led to UK border controls being in Calais was a bi-lalteral agreement.

In a tweet, he said: “David Cameron is doing anything he can to distract the British people from his disastrous, shambolic, pathetic EU deal.”

However, Dover MP Charlie Elphicke also endorsed the PM's warning, saying: “This treaty is extraordinarily important to our border controls. We need to remember it was agreed because of Sangatte [an earlier migrant camp] and if it was scrapped it would be a disaster. We work very well with the French with our border controls in place in Calais.”

Mr Cameron is expected to warn that if Britain leaves the EU, France will stop allowing UK officials to conduct the checks in their country.

Cameron gets his retaliation in first on Calais migrant camps - analysis by our political editor Paul Francis

A Downing Street source told The Telegraph: "The French would love to pull out of the arrangement. "We will be telling people - look, if we leave the EU the Jungle camp in Calais will move to Folkestone. That is not something people want."