The government says asylum applications have fallen by half

P&O, the largest operator of ferry services from Calais to Dover, says up to 60 illegal immigrants are being intercepted each week - more than twice as many as 12 months ago.

British and French authorities tried to curb the numbers of refugees trying to cross into Britain when they closed Calais' controversial Sangatte migrant camp last year.

But reports say asylum seekers are instead massing in Calais' streets waiting to board UK-bound trucks after nightfall.

Spokesman for P&O, Chris Laming, said: "We have definitely seen an increase in numbers trying to board our ferries. We are currently picking up between 50 and 60 a week at the point of embarkation.

I would not say they're back. They never went away Chris Laming, P&O

"We very carefully check every freight vehicle boarding our ferries. Since 2000, we have been employing a team of 40 security staff to carry out checks using CO2 monitors at the point where lorries actually board the boats, at a cost of �1m a year.

Mr Laming said it is well-documented that since the closure of Sangatte there have been "very large numbers of people hanging around the streets and parks of Calais".

"I would not say they're back. They never went away," he said.

Eurotunnel said it had not seen any increase in the number of people trying to use the Channel Tunnel to enter the UK.

Eurotunnel spokesman, Kevin Charles, said: "The days of the mass attempts have long gone. Our security remains extremely high.

Root problem

"We are still using C02 and X-Ray checks and they are working very well."

On Friday, four men were arrested on suspicion of entering the UK illegally after being found underneath an articulated lorry in Nottingham.

The German-registered lorry had travelled to the UK via ferry from Calais.

On Saturday the Home Office announced it had arranged to move sophisticated X-Ray machines from Kent to France to check lorries and cars in a bid to prevent asylum seekers attempting to cross the Channel.

Home Office figures last month showed UK asylum applicants fell to 3,610 in June 2003, less than half of last year's 8,770 applications.