Some blame the surge on improved conditions on the Mediterranean, meaning more people have been able to reach the continent via Libya and Egypt.
Uhrad, 30, an Eritrean accountant who reached the Calais camp yesterday, said that having made it this far they would not be deterred by tightened security.
Summing up the determination at the port he said: "You know people will make a way -- they will dig under the fence. The ferries became too difficult so now they are trying the trains. People will swim if that's too difficult."
By around 2am the port was buzzing with activity, with French riot police watching from a distance, ready to move in when they spotted migrants climbing over or cutting their way through the daunting double fence that is lined with barbed wire at the top, bottom and the space in between.
"I don't care if they put a fire there. I'll still get over it," said 28-year-old Darood, who claims he had fled his native Ethiopia after most of his family members were killed.
He watched keenly as a train carrying lorries lumbered by under the floodlights just a few dozen metres away, about to be swallowed up by the tunnel under the Channel to England.
Darood didn't make it through, but said he would keep trying until he finally did get to the country which he and most of the other migrants in Calais see as some sort of El Dorado where their lives will rapidly improve.
Many have made it, and many more are likely to do so as police admit they are simply overwhelmed by the growing numbers of migrants who have recently turned their attention away from Calais ferry port -- after security was tightened there -- to make their desperate bids at the tunnel terminal.
"It's like trying to swat moles," said Claude Verri of the UNSA police union. "All we can do is take them out of the terminal area and then leave them there. And then five minutes later they can be back inside again."
Exactly how many eventually get to England no one knows, but UK officials say they prevented 18,000 stowaways from entering the country between January 1 and May 21 this year.
Some die in their attempt. At least 10 have lost their lives since June alone, through electrocution or after falling off trains or lorries they were trying to clamber on to.
In the latest death officials said a migrant had leapt on to a Eurotunnel shuttle train but smashed his head on the platform. He died on Tuesday from his injuries.
There is a cat and mouse game between the police and migrants. Every time a hole in the fence is made workers fix it. Lines of officers try to push migrants back toward the "Jungle" -- the vast shanty town among sand dunes several miles away.
There was a moment of tension but the confrontation was mostly good-humoured, with one officer's appeal to the migrants to "Come back tomorrow" met with laughter. "We want to go today," someone shouted back.
"If we had no problems in our countries we wouldn't be here," said Abdurahmen, a young Sudanese man who said he had taken a perilous journey through Libya and then across the Mediterranean on a rickety boat to reach Europe.
"None of us want to live like this. I just want to live in Britain, make a family, take my kids to school," he said. Police said yesterday that overnight they had "arrested" about 300 people trying to break into the tunnel terminal.
But in fact all they do is take migrants who have breached the fence -- or tried to -- and put them on a bus that at dawn deposits them at a roundabout on the edge of Calais.
From there they head back to the Jungle and rest for the day before planning their next assault on the terminal.
The massive migrant presence, combined with wildcat strike action by ferry workers, has crippled Calais and caused travel chaos for holidaymakers and truckers alike as ferry and train services are repeatedly brought to a halt.
Many people of Calais express sympathy for the plight of the migrants -- many of them women and children -- but say their town has suffered enough and the crisis must be resolved.
"Calais is suffocating. The tourists have stopped coming here because all they see on the telly is stories about migrants and they are afraid to come," said Gilles Duvauchelle, the owner of a cafe in the town centre.
Several customers at the bar nodded in agreement, with one woman saying that Britons used to come in large numbers to stock up on wine and French food in the hypermarkets on the edge of town. But now they have dwindled to a trickle, she said.
"The Government is incompetent," said Duvauchelle.
"When migrant camps build up in Paris they move them on. But when they're here in Calais they don't give a damn."
When migrants reach the UK
What happens when an illegal migrant reaches the UK?
If discovered, they are normally dealt with by police while any criminal investigation is carried out. If judged to be an immigration matter, it is passed to the Home Office.
Then what?
They are questioned about their reasons for entering the UK. If deemed to be in the UK illegally (and they do not claim asylum) they are deported.
Where are they detained?
The obvious destination for those arriving from Calais is the immigration removal centre in Dover, but there are 12 centres in the UK.
What if someone claims asylum?
They are detained or granted temporary release while a decision is made.
How many are making it across the Channel?
In the five weeks from the start of June, more than 400 immigrants were found by British police hiding in vehicles or trains. As many as 148 are thought to have reached Britain on a single day last month.
4000
Estimated migrants currently camped out around Calais.
100-150
Migrants who arrive in Calais every day.
700
Migrants from Calais granted asylum in France last year.
1200
Migrants from Calais deported from France last year.
34
kilometres between Dover and Calais
£12m($28.5m)
spent by Britain reinforcing borders in Calais.18,170Stowaways trying to get to Britain between January 1 and May 21, 2015.
- AFP, Telegraph Group Limited
