David Cameron is expected to warn that voting for a "Brexit" would result in migrant and refugee camps springing up across the south-east of England, according to the Daily Telegraph.
The Prime Minister is expected to make national security issues the centrepiece of his mission to keep the UK in the European Union, the newspaper says.
Mr Cameron will apparently suggest that if Britain were to exit the EU, refugees and migrants wouldn't meet a UK border official until they arrived on British soil.
Under current agreements - signed in 2003 - Britain is allowed to carry out border checks at French ports rather than British ones.
Cameron is expected to warn that if Britian leaves the EU, France will cancel the deal.
"The French would love to pull out of the arrangement," a senior Conservative source told The Telegraph. "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."
"Our border currently starts at Calais," the source said. "If we are forced to abandon that, there will be real problems. What's happening in Calais will stop being a problem for the French and become a problem for the UK."
However, the 13-year Le Touquet treaty that allows British passport checks on French soil at Calais isn't strictly linked with the UK's EU membership.