A steel box 7 meters long has been erected on a platform at the station, inside which is a millimeter wave scanner capable of detecting items concealed beneath a person's clothing.

The security system is to be tested at Paddington for four weeks, during which time randomly selected passengers will be asked to participate.

It will take passengers around 80 seconds to pass through the security box, during which time their baggage will also be scanned by an X-ray machine.

On entering the box, the passenger will pass into the scanner, where they will be instructed to place their feet in footmarks on the floor and raise their arms in the air. A robot-like body image of the passenger will be transmitted to a screener, sitting in a booth in the far corner of the box.

If necessary the passenger or their luggage can then be searched by hand.

When first announcing the trial in November, Transport Secretary Alistair Darling made clear it was not considered feasible to introduce airport-style security on London's transport network because of the sheer volume of passengers.

He told a transport conference in London: "You just simply couldn't have people queuing up for hours to get through -- you would be doing the terrorists' job for them. What you can do is ask yourself whether, on a selective basis, at a point where it is appropriate, it could help to make things safer and reduce the risk."

Rebecca Cox, director of counter-terrorism and resilience at the Royal United Services Institute for Defense and Security Studies, said that while the body scanner could be effective, it could only be used in areas where the volume of passenger traffic was relatively controllable.

At present, the scanner is being tested at the Paddington platform for the express train to Heathrow Airport, which sees relatively low traffic. The scanner would be "unworkable" at an everyday rail or underground platform, she told United Press International.

Copyright 2006 by United Press International