A high-tech body scanner for detecting would-be terrorists has been unveiled at London's Paddington station ahead of a four-week trial.
The scanner can detect items concealed beneath clothes
Passengers will be randomly selected to pass through the seven-metre box at the Heathrow Express platforms, while baggage is also screened.
There will be further trials at other mainline and Tube stations.
The move comes in the wake of the 7 July London bombings, in which 52 members of the public were killed.
The trial is to test the equipment and is not regarded as a security move, but could eventually lead to use of the equipment as an anti-terrorist measure.
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But the government has previously said full airport-style security is impossible at UK stations because of the huge numbers of people using them every day.
It will take passengers about 80 seconds to pass through the scanner at Paddington, west London.
It can detect hidden weapons and explosives and was developed by an American company.
Other technology being tested includes advanced closed circuit television systems programmed to sound an alarm when they spot suspicious behaviour.
Tests at London's Liverpool Street station in 2003 led to too many false alarms, but a more sophisticated version is being tested in New York.
Transport Secretary Alistair Darling unveiled the trials in the autumn.
It followed a three-day conference which examined transport security in the wake of the 7 July bomb blasts, in which 56 people, including four suicide bombers, died and 700 were injured.