Jihadis are infiltrating migrant gangs heading for Calais in the hope of entering Britain, according to French police. Forty specialist officers have been tasked with searching for IS fighters among thousands of North Africans travelling across Europe.

A spokesman for the Prefect of Calais told the Daily Express: “There is full and complete vigilance in Calais with regard to threat by jihadists or other criminal networks with potential involvement in people smuggling.

“All our resources are being directed towards detecting and eradicating any network whatsoever. Our priorities are the networks, the individual smugglers and the jihadist potential threat.”

French authorities have long struggled with the number of illegal immigrants heading camped at Calais. At the weekend officers had to be sent into one of the camps when around 200 Sudanese and Afghans began brawling after a mobile phone was stolen.

Under the Schengen Agreement there are almost no borders across the EU. When refugees land in Italy they are left unchallenged until they get to British immigration officers at Calais. Every night the crossing is attacked by hundreds of migrants, desperate to enter the UK.

The security situation is so poor the UK authorities donated the ring of steel used for the G8 summit in Cardiff at the Port of Calais. The extra security has not put the refugees off because they are able to try night after night without facing any punishment.

Last month UKIP’s Nigel Farage warned of a “real and genuine threat” to Europe from jihadis. At the time his concerns were ignored by the European Union, as leaders were keen to force member states to take quotas of migrants. His fears were realised last week when a known terrorist was arrested in Milan.

Charities estimate there are 3000 people living in temporary camps around Calais.