Several new high-tech systems which could help identify potential suicide bombers are being tested on the rail and Underground networks, Alistair Darling, the Transport Secretary, said today.

But Mr Darling told a security conference in Central London that it would not be practical to introduce airport-style passenger-scanning across the whole rail network, despite the July 7 suicide attacks which killed 52 London commuters.

"Our aim is to reduce the risk from international terrorism so that people can go about their business freely and with confidence," Mr Darling said.

A "millimetre wave" scanner which can screen for concealed weapons and traces of explosives will be trialled on the Heathrow Express from Paddington station in West London in the New Year.

Mr Darling said that tests of sophisticated CCTV technology, including a so-called intelligent vision system which can automatically spot suspicious behaviour, are already under way.

Baggage reconciliation, which involves rail and Tube staff asking passengers to account for any suspicious items of luggage, is also being looked at.

Mr Darling said that a range of measures were needed to reduce the risk of another terrorist strike on the transport network, whilst still allowing people to go about their daily lives.

"Of course, we are continuing to learn the lessons of post-July 7," Mr Darling said. "On trains and Underground systems - more varied security measures, high-visibility policing, baggage reconciliation trials, beefing up CCTV.

"We also need to make sure that as new technologies are developed they are tested to see how they can help. So we will test existing and new technologies to see how they might work on the rail and Tube, for example passenger screening and participating in work on intelligent vision systems."

He added: "We are facing a situation unprecedented in recent times. Right across the world - don’t kid yourself it is just here or in the West - we face people who are prepared to kill. We will deal with this threat and we will win. But it needs single minded determination to do that."

Mr Darling said it was impossible to replicate airport-style security on the Tube or rail network, pointing out that London Waterloo station alone handled four times as many passengers a day as Heathrow.

A small number of randomly-chosen passengers will be asked to take part in the tests of the scanning equipment at Paddington station over a four-week period. This will involve them going through an X-ray machine or being searched with a body scanner or sniffer dogs. Luggage could also be put through the scanner.

"What we are trying to find out at the moment is does this piece of equipment, which has been trialled at Heathrow’s Terminal 4, which is a completely different environment to a mainline railway station, can it work?" he said.

"If it can work we will then decide whether it should be used on a selective basis, whether there is any particular railway which may give us cause for concern or bit of the network that we may want to use it on.

"But there is no question of us doing airport-style security on the railway network, it just isn’t practical. If there is... new stuff coming on the market then we would be foolish to reject it out of hand."

Mr Darling refused to say where trials of the new intelligent CCTV system were taking place. It works by alerting staff to behaviour which is either unusual or suspicious, but Mr Darling said it was still in the early stages of development.

The two-day conference, hosted by Transport for London, will hear presentations on the lessons learnt from the July 7 attacks with presentation by senior Underground and London Buses officials and the British Transport Police.

The head of the Madrid Metro system is also expected to address the conference, outlining the steps that have been taken to prevent further terrorist attacks in the Spanish capital, where 191 people were killed and at least 1,800 injured by ten coordinated bombs on packed commuter trains last month.

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