A higher proportion of British Muslims are radicalised than those in several other major western European nations, according to a US research body.
Many British Muslims have a poor view of the West, survey concludes
Muslims in the UK are more likely to see a conflict between being devout and living in modern society than in France, Germany and Spain, it found.
Thousands of people in 15 countries were questioned for a poll for the American Pew Research Center.
In Britain 902 residents took part in the survey in April and May.
Of British Muslims taking part in the poll, 77% said the rise of Islamic extremism worried them.
However, almost a quarter thought suicide bombings and other violence against civilian targets to defend Islam were justifiable - though among these some stated that this was rarely the case.
Andrew Kohut, director of the Pew Research Center, said: "British Muslims were the most radicalised."
The French Muslims were the most temperate, he said.
The Pew Global Attitudes Report found 47% of the British Muslims questioned said there was a conflict between being devout and living in modern society.
That compared with 36% of Muslims in Germany, 28% in France and 25% in Spain.
More than half of the British Muslims, 56%, believed Arabs were not responsible for the 9/11 terror strikes.
Some 69% ascribed three or more negative qualities to Westerners.
Only 47% of the German Muslims, the next highest figure among the European countries, were that critical.
In every negative characteristic they were asked about, British Muslims were the most likely to associated it with Westerners.
Some 67% saw them as selfish, while 64% attributed them with arrogance and 63% highlighted greed.
Another 57% thought Westerners were immoral, 52% said they were violent and 44% labelled them fanatical.
British Muslims were also the least likely to believe that Westerners were respectful of women.
'Mutual worsening perception'
Inayat Bunglawala, of the Muslim Council of Britain, said events of the past 12 months had seen relations between Islam and the West deteriorate.
"Over the past year there has been a mutual worsening perception between Western countries and the Muslim world," he told the BBC News website.
"This is because of a number of events, including the July 7 bombings, the continuing instability in Iraq, the worldwide rioting over the cartoons of the Prophet Mohammed and the continuing threat against Iran.
"The UK helped the US in Iraq, and it's perhaps soured relations more than it would have done otherwise."
But Mr Bunglawala said the large number of Muslims concerned about the rise of Islamic extremism was a positive sign.
"The support for Bin Laden and Al Qaeda is dwindling. Bin Laden has been making regular calls for support but the poll would suggest Muslims are tiring of this tactic and are recognising the harm it does to the image of Islam.
"The statistic of 56% of Muslims believing an alternative explanation for 9/11 might seem shocking.
"But as we see a number of cases coming to court of British Muslims allegedly engaging in acts of terrorism and more convictions, there will be an increased realisation amongst British Muslims that there is a problem with a tiny minority of that group.
"And people are always willing to believe conspiracy theories. In France, a book which said the Pentagon was hit by a missile and not an airliner was a best-seller and forty years after Kennedy was shot, conspiracy theories are still being put forward."
A total of 24% of the British Muslims questioned thought there were times when suicide bombing was acceptable.
That figure broke down into 3% who said it was often justifiable, 12% who said only sometimes, and 9% who thought it was only rarely acceptable.
In France 35% of Muslims thought suicide bombings were justifiable - often, sometimes or rarely. The figure was 21% in Spain just 13% in Germany.
One of the report's authors, Richard Wike, said: "There are some areas where the British Muslims do stand apart a little from the other Europeans we surveyed."
He added that the researchers had not examined why that might be but wanted to dig deeper to find out.