Police and transport officials are also considering installing the equipment permanently at stations across the network. The technology is already used to catch illegal immigrants who hide in lorries at Channel ports but has not previously been used on the Underground because of the high cost and concerns about privacy.

The scanners can spot the waistcoat bombs usually worn by suicide bombers and automatically send an alert to nearby officers. Unlike other scanners, they can cover crowded entrances without the need for people to be stopped for individual checks.

The system works by measuring the solar radiation reflected by people’s bodies and measuring anything which interferes with the reflection.

It can be linked to closed- curcuit television cameras that will automatically pick out and follow a suspect until he can be stopped and questioned.

QinetiQ, the privatised former Defence Evaluation and Research Agency which developed the technology, said the scanners could be fitted to all 270 Underground stations within 18 months.

Each station would cost from £150,000 to £2 million to fit depending on its size and the number of entrances.

Simon Stringer, managing director of QinetiQ’s security division, said: “We have been asked to deploy some of this equipment.

“It would certainly assist in preventing this sort of thing from happening again.

“After today, I expect the travelling public will be more prepared to put up with a greater level of surveillance.” Mr Stringer said.

Philip Baum, managing director of the security consultancy Green Light, said the advantage of millimetre wave was its ability to scan large numbers of people simultaneously and produce an instant moving image. He said that conventional airport scanners were impractical because the Tube handled three million passengers a day.

“As the Israelis have found, if you cause huge queues for security checks you merely create prime targets for terrorists. They just detonate their bombs in the queues.

“But there will be huge civil liberties questions because you will have to accept that people will see you walking round semi-naked.”

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