The UK Daily Mail has reported that a BBC-sponsored survey found that about 15% of Americans and British believe that the US did 9-11 (2011): “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 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.” [1].
[1]. Alanah Eriksen, “One in seven believe U.S. Government staged the 9/11 attacks in conspiracy. The belief is more common among younger people, with a quarter of 16 to 24-year-olds subscribing to the theory”, Daily Mail, 29 August 2011: http://www.dailymail.co.uk/news/article-2031325/One-seven-believe-American-Government-staged-9-11-attacks-conspiracy.html .