Expectations are that Cameron will make national security issues key in his campaign to keep Britain in the EU. | Georges Gobet/AFP/Getty Images David Cameron: Brexit will bring ‘Calais Jungle’ to Britain

British Prime Minister David Cameron is to warn that if the U.K. leaves the European Union, refugee camps will move to the south-east of England because France may no longer allow British officials to make border checks in Calais.

"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”, a senior source told The Telegraph.

Under the current bilateral agreement between the U.K. and France, Britain is allowed to carry out border controls at its French borders, which means that illegal migrant checks on traffic heading to the U.K. take place in the French port of Calais, not in Dover on the British side of the Channel.

Rob Whiteman, the former head of the U.K. Border Association, said in an interview with BBC Radio 4's Today program that Cameron was right to be concerned.

"The bilateral treaty takes a lot of work on the French side to maintain and I think it is almost certain that if we did leave the EU the treaty would come to an end. It is not a foregone conclusion but I think it is fair for the prime minister to claim that the French would almost certainly bring it to an end," he said.

Cameron is in the process of renegotiating British membership of the EU. The issue will be discussed when EU leaders meet in Brussels next week. He will then hold a referendum on the U.K.'s membership of the EU, possibly as early as June.