The belief is more common among younger people, with a quarter of 16 to 24-year-olds subscribing to the theory.
One in seven people are convinced that the U.S. government was involved in a conspiracy to stage the September 11 attacks which killed nearly 3,000 people.
A survey, which interviewed 1,000 people in the UK and the same number in the U.S., found that 14 per cent of Britons 15 per cent of Americans think the past administration was involved in the tragedy.
They were asked: ‘It is generally accepted that these attacks were carried out by Al Qaeda. However some people have suggested there was a wider conspiracy that included the American government. Do you, yourself, believe that there was a wider conspiracy, or not?’
The belief that there was a conspiracy was more common among younger people, with a quarter (24 per cent) of 16 to 24-year-olds subscribing to the theory.
About two thirds of those polled – 68 per cent – said they didn’t think there was a conspiracy.
The survey was carried out for a BBC documentary which examines why so many people believe there is a darker truth behind the attacks.
The survey was carried out by Gfk NOP as part of a BBC Two programme, The Conspiracy Files – Ten Years On.
Telephone polls in the UK and the US were carried out last month.
American radio host and actor Alex Jones is a vocal advocate about the conspiracy theories.
BBC Radio 2 quoted him as saying this morning: ‘Private, corporate, world networks working in US, British, Israeli intelligence – all three groups – have been found to have fingerprints but the main driver was rogue networks at the top of the US Government.
‘The Government admits they’ve staged events before. The official story doesn’t add up.’
The view is taken despite a series of official inquiries which have found no evidence to support the claims.
TOP 9/11 CONSPIRACY THEORIES
1. Why did the world’s most powerful airforce fail to intercept any of the hijacked planes?
What the conspiracists say: The US Vice President Dick Cheney ordered the military to stand down and not intercept the planes.
Official reports say: The transponder, which provides the exact location of the plane, had been turned off or changed.
There was a lack of communication between the civilian air traffic control (FAA) and the military and the military’s equipment was outdated, designed to look out over the ocean to deal with a Cold War threat.
2. Why did the Twin Towers collapse so quickly, imploding without damaging surrounding buildings, after short fires on a few floors?
What the conspiracists say: The Twin Towers were destroyed by controlled demolitions.
Official reports say: The planes severed and damaged support columns and dislodged fire-proofing. About 10,000 gallons of jet fuel drenched the towers, starting the fires. Temperatures of up to 1,000C caused the floors to sag and the perimeter columns to bend, causing the sounds of explosions.
Controlled demolition is carried out from the bottom floors whereas this collapse started at the top.
3. How could an amateur pilot fly a commercial plane in a complicated maneuver, crash it into the Pentagon, 78 minutes after the first report of a possible hijack and leave no trace?
What the conspiracists say: The aircraft was not under the control of al-Qaeda but the Pentagon itself.
Official reports say: There is a large amount of video and still photography showing the plane wreckage and evidence of its flight path, such as broken lamp posts.
4. Why was the United Airlines flight 93 crash site at Shanksville, Pennsylvania, so small and why was the aircraft debris not visible?
What the conspiracists say: The plane was shot down by a missile and disintegrated in mid air, scattering the wreckage over a large area.
Official reports say: There are clear photographs showing aircraft wreckage and the cockpit voice recorder proved passengers had revolted and the hijackers had deliberately crashed the plane.
Another theory was based on a quote from the local coroner, Wally Miller, who said he stopped being a coroner after about 20 minutes because there were no bodies. But he also said he quickly realised it was a plane crash and there would have to be a large funeral service for the many victims.
5. How could the World Trade Centre 7 building, which was not hit by a plane, collapse so quickly (2.25 seconds) and symmetrically, when no other steel-framed skyscraper has collapsed because of fire?
What the conspiracists say: The building was destroyed by a controlled demolition using both explosives and incendiaries.
Owner, Larry Silverstein, was heard saying ‘pull it’ in a TV interview but he was talking about pulling firefighters back.
Some scientists examined four dust samples from Ground Zero and claim to have found thermite, a material which reacts when heated up, and that had been explosives rigged inside.
Official reports say: The building collapsed because of uncontrolled fires, started by the collapse of the nearby North Tower, which burnt for seven hours.
The mains water feeding the emergency sprinkler system was severed.
The thermitic material is a type of primer paint.
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