Labour's candidate for London mayor said on Thursday that "most British Muslims" have met people with extremist views.
In a speech to the Westminster press gallery, Sadiq Khan, the MP for Tooting and a former Labour minister, stressed the importance of integration between different communities in the UK.
In remarks that risk a backlash from the Muslim community, Khan, who previously worked as a human rights lawyer, said: "Most British Muslims have come across someone with extremist views at some point – and so have I. It's affected my personal life, my friendships, and my career.
“People I knew as a boy have gone on to hold extremist views, and even to act on them in terrible ways. When I was a lawyer, as well as representing people who were badly treated by the police or their employers, I sometimes had the unpleasant job of representing people with extremist views.
“It was horrible – but it went with the job. I’ve lost count of the number of times I’ve had to challenge the hideous views of seemingly intelligent and articulate people.
“People who look and sound like normal Londoners, until they say that 9/11 was a Mossad conspiracy. That the Jewish workers in the twin towers were tipped off and escaped."
Khan also argued that British Muslims had a "special role" to play in tackling extremism.
"A special role not because we are more responsible than others – as some have wrongly claimed," he said. "But because we can be more effective at tackling extremism than anybody else.
"Our role must be to challenge extremist views wherever we encounter them, to challenge this perverse ideology and to insist that British values and Muslim values are one and the same."
In a very personal speech, Khan referred to occasions he had been faced by extremists while out campaigning. During the 2010 general election, when campaigning in his south London constituency, people turned up outside the mosque and told the congregation that they would go to hell if they voted.
As a result of threats he has received, he has had to consider police protection for his two daughters, he said.
The mayoral hopeful also said he was worried his daughters "could be groomed by extremists on the internet".
He said this was a concern for all Muslim parents in the West, especially after a series of young people fled their homes and travelled to Syria.
Khan argued that successive governments allowed radicalisation to "thrive" by not doing enough to stop segregation in British communities.
"Too many British Muslims grow up without really knowing anyone from a different background," he said. “And too many British people have never befriended a Muslim. Never worked together, never eaten together, never played sports together."
Khan also made a concerted effort in his speech to draw defining lines between himself and Labour leader Jeremy Corbyn. Following the targeted assassination last week of ISIS killer Mohammed Emwazi in Syria, Corbyn said it would have been better if he had beencaptured and asked about the legal backing for the strike.
But Khan said in his speech that he backed the airstrike. "There is nothing I disagree with in the way Emwazi was taken out. We are safer now," he said, adding that he lived "in the real world".