Scotland Yard said three properties - two in Westminster and one in Barnet are being searched along with a number of cars - after two men were arrested on suspicion of terror offences.
Police said that one of the arrests in Westminster took place at a residential address and not near any major landmark.
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British soldiers will join troops from some 30 countries who work in the country.
The demand comes after the Prime Minister urged a "grown up" relationship between her government and the devolved administrations.
The rapper failed to make it to London in time as he had problems with his passport.