Nine men, including the radical Islamist preacher Anjem Choudary, have been arrested in London on suspicion of being members of a banned organisation.
Officers are searching 18 premises in London and one in Stoke-on-Trent.
The Met Police said it was part of an ongoing inquiry into Islamist-related terrorism and not in response to any immediate threat to the public.
Mr Choudary is the former UK head of the Islamist group al-Muhajiroun or Islam4UK, banned in the UK in 2010.
The arrested men, aged between 22 and 51, are being held at police stations in central London.
Most recently, Choudary sided with the Islamic State, which has beheaded a British citizen. He has been preaching jihad while living on the British taxpayer’s dime for years now. He is a jihadist, straight up, no different than Anwar al-Awlaki or any other jihadist preacher.
If the west had sharper war teeth, Choudary would be dropped into Syria at an ISIS command post just ahead of an allied airstrike.