Socialist Bernard Cazeneuve says tighter security around the Red Cross refugee camp ahead of its closure is driving illegal immigrants heading for Britain along the Normandy peninsula.

Four hundred have been arrested in Cherbourg since the beginning of the summer.

Sangatte near Calais, next to the entrance to the Channel Tunnel, is nearly 200 miles (300 kilometres) north-east of Cherbourg.

There is a mafia of smugglers organised on the port, against whom it would be appropriate to act in an extremely determined manner

Cherbourg mayor Bernard Cazeneuve

The channel port has previously been untouched by the problems of illegal immigration.

But smugglers are now said to be looking for softer targets since France and Britain reached an agreement to close the Sangatte camp next year.

BBC correspondent Jon Sopel witnessed one pulled out from between two rear wheel arches by a guard dog.

He says small huddles of immigrants wander the town late at night and at dawn, hoping to stow away on lorries bound for Britain.

Mr Cazeneuve said: "There is a mafia of smugglers organised on the port, against whom it would be appropriate to act in an extremely determined manner."

They "dangle the prospect of passage to Britain to refugees with very little money, for sums that bear no relation to what refugees can pay," he added.

New laws

Mr Cazeneuve and other angry elected officials from Cherbourg demanded tougher measures from the interior minister in Paris on Wednesday.

Nicolas Sarkozy promised to deploy a group of paramilitary police and about 15 extra interpreters and border officials in Cherbourg, increase patrols and install new perimeter fencing.

Mr Sarkozy also vowed to push through new laws to crack down on illegal immigration "as soon as Parliament resumes work after the summer recess", according to Cherbourg council president Jean-Francois Legrand.

But other Channel ports are now on a high state of alert, in case the problem spreads.