“London Calling” the graffiti at the so-called Jungle Camp in Calais where around 4,000 migrants live in makeshift tents and shipping containers, desperate ticket to Britain.

Under a 2003 agreement, British border checks are performed on French soil in Calais, which keeps the migrants in France.

Speaking Monday, British Prime Minister David Cameron warned that deal would be threatened if Britons voted to leave the European Union.

“There are a lot of opposition politicians in France who would love an excuse to tear up that treaty and would like the border not to be in France, but to be in Britain and I don't want to give people an excuse to do that.”

Border police and migrants play a constant game of cat and mouse in Calais's port.

Migrants try to sneak into trucks as they board ferries bound for Britain or even break into the tunnel that carries trains beneath the Channel.

There is also growing tension between migrants and local public.

Members of the anti-Islam group PEGIDA which was founded in Germany, attempted to stage a march in Calais Saturday, despite local authorities banning all public protests.

“These people do not want the common good;they just want to exploit poverty and anger and they have no place in Calais.”

In recent weeks, the migrant camps have been hit by snow and winter storms.

Doctors Without Borders, the only major charity working around Calais, says conditions at one camp near the town of Dunkirk desperately need to be improved.

“There are about 2,500 people living there at the moment, mainly Kurds from Iraq and from Syria.

And the conditions in that camp are really horrific.

People are living in this kind of muddy wasteland.

There are rats; the people are getting scabies because of poor hygiene.”

Doctors without Borders successfully lobbied for a new camp to be built in Dunkirk, which is due to open later this month.

The longer-term fate of the camps, and of its residents, could depend on Britain's choice widely expected later this year to stay or leave the European Union.