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 has told MPs.
But after addressing the Commons home affairs select committee on Tuesday, 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.
Ms Dick, who is head of specialist operations for the Met, said police officers have taken statements from 60 members of the public who are "significant witnesses" in the Woolwich investigation.
Twelve people have been arrested, of whom two have been charged and two released with no further action. The remaining eight are on bail.
She said the investigation is being run by Scotland Yard with the "very strong" support of the security services and other agencies.
Choudary has made several media appearances since the death of Drummer Rigby on 22 May, and refused to condemn the young soldier's murder.
Speaking after the hearing, Ms Dick said the force works with the CPS to ensure that officers understand technical areas of law governing terrorism and incitement to racial or religious hatred.
She added: "It is fair to say that many so-called preachers of hate are very familiar with criminal law."
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