Scotland Yard is closely watching radical cleric Anjem Choudary to see if his proclamations break the law, one of the force's most senior officers told MPs today.
But after addressing the Commons home affairs select committee, Assistant Commissioner Cressida Dick warned that "so-called preachers of hate" are often familiar with the law.
Her comments came amid reports that Choudary has made controversial remarks about the murder of father-of-one Drummer Lee Rigby near Woolwich barracks.
The former spokesman for the now-banned Islamist group Islam4UK, who admitted knowing one of the men charged with the soldier's murder, is also understood to be receiving police protection outside his east London home.
Asked by committee chair Keith Vaz if the Metropolitan Police is providing protection to Choudary, Ms Dick said: "We constantly risk-assess what's going on around a number of different people who have high profiles in the media.
"In the case of somebody like Mr Choudary, we are constantly assessing, of course, whether any of his proclamations are breaking the criminal law and working with the CPS to ensure that if he is breaking the criminal law we know about it very swiftly."
She added that if officers fear someone's "life is at risk or indeed that there's going to be a major disorder around them", then they may put a police presence in place.
Her evidence comes after two men - Michael Adebolajo, 28, and Michael Adebowale, 22 - appeared in separate courts yesterday charged with Drummer Rigby's murder.
Ms Dick told the committee that at its peak the Woolwich investigation had 600 officers employed directly, including 100 from its national counter-terrorism network.
Officers have searched 17 addresses and six cars, she added.