Only four per cent of British Muslims believe Al Qaeda was responsible for the 9/11 attacks in the U.S., a study has found.

In a poll that researchers called “deeply troubling”, nearly a third thought the American government was behind the attacks, while another 7 per cent thought it was a Jewish conspiracy. The majority, 58 per cent, said they did not know who was responsible.

Researchers for the Policy Exchange think tank said it was “a cause for concern” that so many British Muslims were willing to “entertain wild and outlandish conspiracy theories”.

ICM, who carried out the survey for the think tank, also found that nearly half said they would not support someone to the police if they knew they were involved with supporters of Islamic State and other terror groups in Syria.

Around 40 per cent also said they would support the introduction of sharia law in the UK, while another 40 per cent were in favour of gender-segregated classrooms and 44 per cent said schools should require girls to wear traditional Islamic dress.

The research also found that the Muslim Council of Britain (MCB), often billed as the main spokesmen for Muslims in the UK, reflected the views of the just 4 per cent of those polled.

The MCB responded by issuing a statement accusing Policy Exchange of trying to “delegitimise the organisation”.

Muslim Labour MP Khalid Mahmood wrote in a foreword to the report: “It is obviously a cause for concern that so many within our communities should doubt the very existence of [extremism], even as we face a severe and ongoing terrorist threat.

“Even more startling is the fact that so many British Muslims seem ready to entertain wild and outlandish conspiracy theories … believing that dark forces are at work to “do us down” as Muslims.

“It is deeply troubling that this seems to have led a not-insignificant minority to believe that the world is at the mercy of the machinations of dark, anti-Muslim forces.”

The research did find, however, that more than half of Muslims expressed a desire to fully integrate with non-Muslims, while 93 per cent said they had a strong attachment to the UK.

Mr Mahmood said this showed the group were among the most “loyal, patriotic and law-abiding citizens.”

A similar poll in April found that half of British Muslims thought that homosexuality should be illegal, while four in five thought wives should always obey their husbands.

Trevor Phillips, the former head of the Equalities and Human Rights Commission (EHRC) warned Muslim immigrants were creating a “nation with a nation”, however the left-wing Guardian spun the poll as showing Muslims felt a “strong sense of belonging”.

It said the poll “suggests that in most cases attitudes held by the British Muslim population do not broadly differ from those held by the population at large.”