Some say human trafficking is as profitable as drug trafficking

It is estimated that some 400,000 people a year enter the EU illegally.

The main reason for the upsurge has been the opening up of Eastern Europe combined with the tearing down of internal EU borders under the Schengen agreement.

There are several favourite routes in - via boat from Albania, Tunisia or Morocco into southern Europe; from Sarajevo airport via Croatia and Slovenia into Italy and Austria; or overland starting from Istanbul and often ending up in Germany.

And, recently, a new route from Russia into Finland has opened up.

Risky journey

Many of those smuggled in are Afghans, Albanians, Kurds, Bangladeshis, Iraqis - and, increasingly, Chinese.

Dead stowaways have been found before at Dover

But there are risks. At least 173 people drowned last year in the Adriatic attempting to cross from Albania to Italy.

Two years ago, 90 Romanian illegal immigrants were rescued from a locked lorry in Italy suffering from asphyxiation.

And just before that, in a incident similar to the one at Dover, dozens of Sri Lankans died after a driver left them locked in a container lorry at the Austro-Hungarian border.

Organised crime

One reason the EU is so concerned is the involvement of organised crime.

Europol says gangs are making as much from human trafficking as they are from drug smuggling.

Often the immigrants spend thousands of dollars to be smuggled into the EU only to be conned and dumped elsewhere.

The EU is aiming to harmonise aslyum seeking legislation but the question of how to patrol its vast borders effectively remains as difficult as ever.