The immigrants stuffed into car seats and under bonnets trying to get into Europe

In one image, two men have managed to hide themselves inside the front seats of a Mercedes, with their heads jammed into the plastic head rests.

With a pair of human-traffickers sitting right on top of them, on the hollowedout seats, the immigrants had hoped to be smuggled into Europe.

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Their plan failed however and the men were all caught at a border crossing in the Balkans.

A second image shows a man hidden under the bonnet of a car with his body curled dangerously around the engine.

In a third, an illegal immigrant has had himself buried within a car's dashboard.

Border guards have also come across immigrants wedged inside suitcases or hidden in other secret compartments in the back-seat areas of cars.

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The pictures show the methods used by human-trafficking gangs who control a trade estimated by the United Nations to be worth more than £4billion a year.

All the photographs are understood to have been taken at frontiers in and around the Balkans during the past year.

They were sent to UN investigators and circulated in a package marked "No Visa Required".

Kosovo and Bosnia - which have many unmanned border crossing points - are two of the main land transit routes for people traffickers. Scroll down for more

Massive efforts have been made in both territories to tighten the borders but officials admit they remain gateways to the West. Britain and Germany are the destinations of choice for the immigrants.

Illegals pay up to £10,000 to be smuggled into Europe, leaving them and their families in debt for years to come.

It is thought that 50,000 illegal immigrants passed through the Balkans last year alone. Border checks are becoming increasingly effective, however, and guards can call on machines that will detect a human presence anywhere in a vehicle.

This has forced the people-smugglers to take greater risks with their clients' safety or even abandon them once they have received payment.

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In Bosnia, one group of illegals was shown a lake, given a boat and told Italy was a two-hour row away. They were arrested by police waitingat the far side of the lake.

"The racketeers are exploiting what is a huge market and they treat human life as a commodity," one senior investigator told the Mail yesterday.

"This is illustrated by these pictures. There is little regard for human life or dignity. These people should be seen as victims. If they don't go into the hiding places, they are told they will simply be abandoned and never make it.

"They have no choice and the traffickers know that." Officials say the hiding places in these photographs would have been used by immigrants at borders and police checkpoints only.

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Investigators say that reports of "amnesties" for 100,000 asylum seekers in Britain are being used by people-smugglers to drum up business.

In a controversial move, the Home Office is to allow a further 165,000 aslyum seekers whose files have been forgotten to allow to stay in Britain.