Dover-bound migrants filmed sitting on lorry axles
Migrants have been filmed sitting on the axles of lorries in a desperate attempt to enter the UK from Calais.
Cameras installed by the BBC have captured men running towards trucks and climbing beneath the vehicles, with drivers oblivious to their actions.
Two migrants were recently killed in attempts to get to Dover.
Immigration Minister James Brokenshire said there had been an "increase" in people trying to get into the UK through the Channel ports.
This was mainly due to conflict in the Middle East and North Africa, he explained.
Lorry driver Clive Mills, whose truck had been used by migrants, said: "I would never have known they were on there. I didn't even see them get on.
"I was looking in the mirror, looking down the road to pull out - it's just frightening.
"Something somewhere has to change because you can kill people."
Mr Mills had allowed BBC South East Today to film his lorry as he drove to the port.
The BBC's cameras were attached to another lorry, which stopped as soon as the migrants were filmed, so as not to endanger their lives. French police were also called.
Speaking to BBC South East after being shown some of the footage, David Cameron said: "We are strengthening our borders, we're returning more people who get here illegally.
"We've invested in the UK Border Force that's doing a good job and we're also making sure that people who come here can't immediately claim benefits."
"Immigration is a major concern for people in this country and it's a major concern for me," the prime minister added.
Colin Campbell, BBC South East Today's home affairs correspondent, said gangs of migrants swarm up on to the approach road into the port as lorries approach.
"Calais is again experiencing a surge in migrant numbers," he said.
"Many Syrians are now arriving here - they say they've fled war and persecution.
"Others have come from Afghanistan, Iraq, Libya and Eritrea.
"There's estimated to be more than 400. Most are sleeping amongst squalor in the largest makeshift camp right next to the port."
After one migrant was seen climbing on to a truck, and was told he was risking his life, he said: "I know, but I have to go there.
"This country is not good to live in, we have to go to England."
And when told of the risks, another group of migrants said: "We don't care. It doesn't matter. We don't care anyway.
"I'm sorry, I'm so sorry... we are sorry."
George Gillas Sallam, a French charity worker who supplies migrants with food, said two had recently been killed and "nothing" was being done.
"They've found a place for them in the cemetery, that's all I think," he said.
"Some bodies have been repatriated, but that's one line in the newspaper in Calais."
Mr Brokenshire said there was a "good working relationship" between the British and French authorities.
"We've invested £2m on additional detection equipment, so that's looking at heart beat detectors, carbon dioxide detectors and also the sniffer dogs as well," he said.
"There have been indications of an increase in the number of people trying to get to the UK through the Channel ports.
"That in part is because of ongoing conflict in the Middle East and North Africa."
You can see more on this story on BBC South East Today at 13:30 and 18:30.