Mak Chishty, who was the country's most senior Muslim officer before retiring last week, issued a "call to action" for a show of defiance against fanatics online.
Outlining his blueprint for tackling extremism in the wake of three deadly terror attacks, the ex Met Police commander also recommended a "mapping" exercise to identify areas of vulnerability and more leadership roles for women.
He described the London Bridge atrocity as a "turning point" and said Britain must face up to "difficult conversations" rather than "skirting round the issue".
Mr Chishty appealed to Muslims of all ages to use their Facebook or WhatsApp accounts to "denounce extremism as not theirs".
He said: "All of a sudden you will find maybe these extremist voices begin to shrink.
"Remove their dominance, starve them of that oxygen, make sure they've got a powerful lobby against them.
"We can do that now, we can do that today. Don't attack me for saying that dangers lie within mosques because they do. Instead, use your voice and maybe avert the next terrorist attack."
The former police officer painted a stark picture of the task facing authorities seeking to address Islamist extremism.
He warned that conspiracy theories suggesting terrorists were not behind recent attacks are going unchallenged while "quite extreme views" are present in a small minority of mosques.
He said a more "straight-talking" approach was needed, arguing that figures in positions of authority have "skirted round the issue".
Mr Chishty said: "Often, we've shied away from difficult issues or government programmes have simply not delivered what they were supposed to.
"The first thing that needs to change is we need to be comfortable with difficult conversations.
"We are not trying to defame Islam - that's the last thing that British people want to do. Let's stop being so sensitive about the language.
"I've said this menace lurks within Muslim communities. I mean that - it does. I'm a Muslim, I'm proud of that. But it doesn't change the fact that actually it's within our own communities."
Mr Chishty outlined a three-month mapping project which would be carried out in order to improve understanding of which interventions should be focused where.
He said: "It's difficult to map extremism ... but you might be able to map areas of the country where (there is) vulnerability, amenability, propensity - the drivers, the factors that might lead people to becoming more radical, more fundamental, even more extreme and more violent with extremism."
Other proposed steps include placing intermediaries in communities to reassure people about contacting the anti-terror hotline, measures to improve support for the Prevent programme, greater strategic and leadership roles for women and the establishment of a new national centre of excellence.
In a speech at the Reform think-tank, Mr Chishty said anti-Muslim sentiment online has been "relentless" following the London Bridge attack while hate crime has spiked.
"The backlash has been something of a different scale," he said.