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Rail and Tube passengers face being screened as new security measures are tested on the UK's transport network. So what can they expect and will it work?
With nearly one billion journeys made last year on the UK's public transport network, any new security measures risk inconveniencing millions of people.
So Transport Secretary Alistair Darling was keen to stress that a sealed, airport-style security system is an impossibility for rail and the Underground, because queues and delays would bring the system to a halt.
A four-week trial, which begins on the Heathrow Express platforms at Paddington station in London in the New Year, will be for passengers picked at random. If the screening is eventually implemented, police intelligence could also play a part in selection.
The trial is voluntary, so if people agree to be screened they will either walk through a scanner or be "frisked" by a hand-held device.
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Millimetre-wave technology, which can detect dense objects concealed under clothes, has never been used on the railway before.
Other equipment being tested includes hand-held trace machines for explosives and X-ray machines to examine bags. Sniffer dogs will also be used to detect explosives.
Different locations involved in the pilot will have different methods, or a different combination of them, and some will not have the walk-through scanners at all.
A Department of Transport spokesman said people with fears the millimetre-wave machines could "see" their bodies and compromise their privacy had nothing to fear. And he was hopeful a check would not take up much time.
He said potential costs depended on what equipment would be picked after a post-trial evaluation.
'It won't work'
Observers have suggested this kind of system could require as many as 20 people for one post over 24 hours, to watch footage and respond. The spokesman said discussions were under way with staff about the implications for them.
"We are testing the new technology. It's only right and proper that the decision is made with equipment which has been tested," he says.
But transport expert Christian Wolmar thinks the trial makes no practical sense and amounts to nothing more than a public relations exercise.
Darling wants to avoid airport headaches
"I just don't see how it can work and nobody in the transport industry does. It's just not a realistic proposition," he says.
"This is a politicians' disease - to be seen doing something. What are they trying to achieve?"
Stop and search powers already exist to pick people at random and passengers could get very annoyed if additional checks meant they missed their train, he adds.
"Terrorists assess risk. They don't take bombs on to planes any more and they may assess this risk and think 'There's nothing significant being done here.'
"We're talking about suicide bombers. Presumably they would blow themselves up anyway and just cause chaos on the concourse."
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