The explosive device smuggled in the clothing of the Detroit bomb suspect would not have been detected by body-scanners set to be introduced in British airports, an expert on the technology warned last night.
The claim severely undermines Gordon Brown's focus on hi-tech scanners for airline passengers as part of his review into airport security after the attempted attack on Flight 253 on Christmas Day.
The Independent on Sunday has also heard authoritative claims that officials at the Department for Transport (DfT) and the Home Office have already tested the scanners and were not persuaded that they would work comprehensively against terrorist threats to aviation.
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The claims triggered concern that the Prime Minister is over-playing the benefits of such scanners to give the impression he is taking tough action on terrorism.
And experts in the US said airport "pat-downs" a method used in hundreds of airports worldwide were ineffective and would not have stopped the suspect boarding the plane.
Umar Farouk Abdulmutallab, 23, allegedly concealed in his underpants a package containing nearly 3oz of the chemical powder PETN (pentaerythritol tetranitrate). He also carried a syringe containing a liquid accelerant to detonate the explosive.
Since the attack was foiled, body-scanners, using "millimetre-wave" technology and revealing a naked image of a passenger, have been touted as a solution to the problem of detecting explosive devices that are not picked up by traditional metal detectors such as those containing liquids, chemicals or plastic explosive.
But Ben Wallace, the Conservative MP, who was formerly involved in a project by a leading British defence research firm to develop the scanners for airport use, said trials had shown that such low-density materials went undetected.
Tests by scientists in the team at Qinetiq, which Mr Wallace advised before he became an MP in 2005, showed the millimetre-wave scanners picked up shrapnel and heavy wax and metal, but plastic, chemicals and liquids were missed.
If a material is low density, such as powder, liquid or thin plastic as well as the passenger's clothing the millimetre waves pass through and the object is not shown on screen. High- density material such as metal knives, guns and dense plastic such as C4 explosive reflect the millimetre waves and leave an image of the object.
Mr Wallace said: "Gordon Brown is grasping at headlines if he thinks buying a couple of scanners will make us safer. It is too little, too late. Under his leadership, he starved the defence research budget that could have funded a comprehensive solution while at the same time he has weakened our border security.
"Scanners cannot provide a comprehensive solution on their own. We must now start to ask if national security demands the use of profiling."
Mr Wallace added that X-ray scanners were also unlikely to have detected the Christmas Day bomb.
The Government is looking at millimetre-wave scanners for widespread use in British airports as part of Mr Brown's review. They are safer to use than X-ray scanners because they do not emit radiation and do not require passengers' consent. Pregnant women cannot go through X-ray scanners but there are no such health risks with millimetre-wave technology.
However, a Whitehall source revealed that the DfT and the Home Office had already tested both the millimetre-wave and X-ray body-scanners as part of an ongoing assessment of airport security and anti- terror measures.
But the security scare has caused national governments and airports to renew their interest in body-scanners. Amsterdam's Schiphol airport, where Abdulmutallab changed flights en route from Nigeria to Detroit, is to activate 17 scanners it bought two years ago for flights to the US, despite EU advice that there are privacy and human rights issues.
Last week the US Transportation Security Administration ordered $165m-worth of scanners, using both millimetre and X-ray technology, from L-3 Communications.
Qinetiq had developed a similar millimetre-wave body scanner, but is now developing a sophisticated "stand-off" scanner which does not pose any privacy issues as it does not show a body image. Materials hidden on a body reflect back signals, showing up as a red alert on screen. Kevin Murphy, product manager for physical security at Qinetiq, admitted this SPO system would also not have picked up the Christmas Day bomb, but insisted that it could be used as part of a "layered approach" to security in mass transportation, which would also include monitoring people's behaviour.
Mr Murphy echoed Mr Wallace's doubts over whether the millimetre-wave body scanners being discussed by the Government would have picked up Abdulmutallab's hidden explosive. He said: "It is conjecture whether or not these methods would have seen through clothing. I don't think anyone knows."
He added: "The solution is to acknowledge that there isn't a single technology out there that is an answer to the whole problem."
Each full body-scanner costs around £100,000. However, opinion is divided among aviation experts. Writing in The Independent on Sunday, Chris Yates, Aviation Security Editor of Jane's Information Group, says: "Body scanning (whether it be millimetre-wave or X-ray based and manufactured by any of the companies in this sector), has a significant role to play in enhancing UK airport security immediately.
"Body scanning is only half the story, though. The Government cannot ignore the liquid aspect any more. Liquid explosive became a high-agenda issue following the thwarted transatlantic bomb plot of 2006 and is clearly implicated in the attempted downing of Northwest Airlines Flight 253. If the Government skirts over this aspect it will be nothing short of a dereliction of duty."
On Friday, in an announcement on the Downing Street website, the Prime Minister said an urgent review of security at UK airports would be implemented.
Promising to react quickly to the "wake-up" call of last week's attempted atrocity, Mr Brown added: "In co-operation with President Obama and the Americans, we will examine a range of new techniques to enhance airport security systems beyond the traditional measures. These could include advancing our use of explosive trace technology, full body scanners and advanced X-ray technology."
A spokesman for BAA, which owns six UK airports, including Heathrow, said on Friday: "Any comprehensive review of airport security should involve government and the aviation industry, and should establish how a combination of technology, intelligence and the profiling of passengers can build a better defence against the unpredictable and changing threat from international terrorism."
Responding to Mr Wallace's claims, a DfT spokesman said: "Body-scanners are being assessed urgently as part of a package of measures to respond to the latest incident. Trials of body-scanners have already taken place and these are being assessed urgently as part of an immediate review of airport security."
In the US, the "pat-down" search used by security staff was derided as ineffective because officials are forbidden from frisking sensitive areas. Analyst Michael Boyd said: "To have people hold up their arms and just pat them like I'm really going to carry a bomb down there. You know where you're going to put it, and no one's going to go there."
Mr Brown has also convened a meeting for 28 January on the terror threat posed by Yemen, where Abdulmutallab is alleged to have undergone terrorist training.
In a fresh announcement yesterday, Downing Street announced an emergency cabinet committee meeting with senior ministers and intelligence chiefs to discuss the UK's response to the attempted attack.
No 10 and the White House have agreed to step up efforts to tackle the emerging threat from Yemen and Somalia.
