The French harbour of Calais is the main gateway into Britain...
for cargo transport over the road.
The big lorries and trucks that cross the border...
seem to be an ideal spot to hide in.
Many migrants try to enter the UK this way.
But British and French customs work together...
to prevent illegal migration into England.
Anyone who is detected, will be sent back.
Can you imagine hiding silently between the cargo for days...
with limited food and water?
The customs have modern equipment to do the checks.
Like carbon dioxide measuring tools.
Your breath contains carbon dioxide. So high ratings may cause your detection.
Right to the front we checked it, and it's all clear. So we're letting the driver go.
And then they have heartbeat detection equipment...
that reveals the presence of human beings in the trucks.
If the machine gives a red warning, they go into action.
We're opening it, because the heartbeat machine detected two reds.
Which means... And then one green.
Which means we're unsure as to what's inside.
Well, you can hold your breath for some time, but to stop the heart from beating...
Sometimes people are so hard to find...
that dogs that are specially trained to smell human presence...
help the officers locate stowaways in the cargo.
He will search a vehicle when I tell him to.
And his indication, if there are people present in the back of the vehicle...
he will freeze, sit and stare...
at the point where he's getting the most amount of scent from the vehicle.
For the moment it's 180.90...
which is twice as high as we'd normally expect in a lorry.
We'll have to open that one.
Yeah, I've got four in here.
You've got three, so it's seven.
22. -They will be detained and processed.
And then we will hand them to the French police.
These stowaways are from Afghanistan.
Later that day, they also got a man from Eritrea.
All were sent back to where they came from.
It's sad, after all that they went through.