AN amazing sensor that can scan huge crowds and pick out a lone suicide bomber by homing in on hidden explosives has undergone official tests, The Sun can reveal.
The revolutionary gizmo - similar to airport scanners but top secret - is believed to silently analyse materials using the unique "terahertz" waves emitted by different substances.
Government scientists began testing it a year ago on mock crowds where one person in every 75 carried a "Person-Borne Improvised Explosive Device" - boffin-speak for a suicide bomb.
Heavily-censored reports obtained by The Sun in a freedom of information request reveal other trials saw the human guinea pigs armed with "handguns and knives".
Real terrorists would have no idea they had been scanned from a distance - and could be intercepted before causing mayhem.
The futuristic device - officially known as a "stand-off imaging system" - could be used to protect plum al-Qaeda targets such as rail stations, shopping centres and sporting events.
Home Office sources have not ruled out the system being in place at the London Olympics.
Details remain hush-hush but it is thought to be sophisticated enough to differentiate between plastic explosive and plasticine. A Whitehall source said: "If this technology had been available years ago, who knows what tragedies might have been averted?"
The tests have been conducted at the Home Office's Centre for Applied Science and Technology (CAST).
It has two secretive labs, one in Hertfordshire and the other in West Sussex. A source said: "It's just like Q's lair in the James Bond films.
"You half expect to see 007's Aston Martin. But the work that goes on there is vital."
The Home Office said: "Protecting the public is our No1 priority. We regularly test new technologies to help us face the ongoing terrorist threat."