It appears that even a terrorist attack where I didn't think one could dispute the official line is indeed doubted by a significant percentage of British Muslims.
I say significant because, as I said, I thought the evidence that British Muslims carried out the attacks was overwhelming, but:
A quarter of Muslims polled think the authorities involved with staging the 7/7 London bombings.
It's a worrying picture that suggests a significant minority of British Muslims are alienated from the government and the security services.
A Channel 4 News survey of 500 British Muslims, carried out by GFK NOP, has found that nearly a quarter don't believe the four men identified as the London bombers were responsible for the attacks.
And a similar number say the government or the security services were involved. Nearly six in ten of those polled believe the government hasn't told the whole truth about the July the 7th bombings - and more than half say the intelligence services have made up evidence to convict terrorist suspects.
...
24% believe the four men identified as the July 7th bombers were not actually responsible for the attacks.
For comparison's sake, another poll revealed that only 17% of BRitish Muslims believe that Arabs carried out the 9/11 bombings (though 13% of British Muslims fully support the attacks):
The Pew poll found that British Muslims are far more likely than their European counterparts to harbour conspiracy theories about the September 11 attacks. Only 17% believed that Arabs were involved, compared with 48% in France.
http://www.guardian.co.uk/world/2006/jun/23/uk.religion
Also interesting to note, a quarter of British Muslims justified the attacks. But that was hardly surprising.