By James Coomarasamy BBC Paris correspondent in Frethun

Earlier this week, I spent the night at the Calais Frethun freight terminal.

Over the past few months, this sprawling, unremarkable depot, just south of the French Channel Tunnel entrance, has become the focus of attempts by would-be asylum seekers to get into Britain.

Every night - come rain or shine - hundreds of young men from the nearby Sangatte refugee centre prowl around its wire perimeter fence, hoping to sneak onto the goods trains that leave from there.

Night after night, the young men try to access the tunnel

On the night that I was there, the gendarmes were out in force.

After some arm-twisting by the British Government, their numbers were beefed up in March, because the immigrants' nightly assaults on the goods yard were causing such huge disruption to the freight traffic through the tunnel.

They still are. Five trains got through on Wednesday night - a relatively high number in the current circumstances, but nothing like the 18 or so which would be crossing to England if things were normal.

It is not surprising that the British rail freight operator EWS is furious - and is keeping a vigilant eye on the comings and going at the yard.

It was EWS who revealed the embarrassing security lapse last weekend, when the special squad of gendarmes was re-deployed and 300 immigrants managed to storm the trains. Several dozen made it through to the other side.

Farcical game

The gendarmes are back now. I counted at least 30 patrolling one part of the long perimeter fence.

The authorities have been distracted by French internal matters

I watched as they set off in small groups, trapping the immigrants with the help of walkie-talkies and sniffer dogs, and bringing them back to a collection point by the side of the tracks.

The whole thing has a farcical air to it, reminiscent of a schoolyard game of tag.

The captured immigrants are brought back to the collection point, where they greet their comrades with a shrug and a smile, then sit on the floor, waiting for buses to take them back to the nearby Sangatte refugee centre.

The following night, they will be there again. This is a scenario that is being repeated to absurdity - a cycle which no one seems willing or able to break.

Domestic political circumstances are not helping matters. France is reorganising its police forces at the moment; it has an interim government - and a number of long bank holiday weekends, when gendarmes like to take leave.

This is thought to be one of the rather prosaic reasons why last weekend's shift change at the freight yard took so long.

Violence fears

But, all the while, local tensions are rising. The residents of the small village of Sangatte - now outnumbered three to one by the immigrants who live in the Red Cross centre there - have been remarkably tolerant until now, but their frustrations came out in the presidential election.

In this part of northern France, particularly large numbers of people voted for the far right leader, Jean-Marie Le Pen.

Not only that, but soon after that vote, youngsters from a neighbouring village drove up and shot some of the immigrants - the first reported incident of its kind.

No wonder that the mayor of Sangatte believes it is only a matter of time before there is what he calls a "dramatic accident".