British radical Islamic preacher Anjem Choudary, who is also known as 'hate preacher', was among the nine men arrested in London on suspicion of being members of a banned organisation.
The arrest comes just days after the man voiced his support to the deadly Islamic State militants in Syria.
Officers raided 18 premises in London and one in Stoke-on-Trent. British news organisations have cited Met Police as saying that it was a part of an ongoing inquiry into Islamist-related terrorism and not in response to any immediate threat to the public.
The nine men, aged between 22 and 51, are being held at various police stations in central London, police said.
A statement by the Met said that the men were arrested on suspicion of being members of a proscribed organisation and supporting the organisation in contravention to Section 11 and 12 of the Terrorism Act 2000 and encouraging terrorism, contrary to Section 1 of the Terrorism Act 2006, BBC reported.
Eleven premises in east London, one in west London, another one in north-east London and five in south London were being raided, the police added. A residential property in Stoke-on-Trent was also being searched.
Choudary is the former UK head of the Islamist group al-Muhajiroun or Islam4UK, which is banned in the United Kingdom since 2010.
The 'hate preacher' has lately expressed his support for the Islamic State militant group in Syria and Iraq while also justifying, on a few occasions, the cruel activities of the jihadists such as beheading or mass killing.
Last week, he said he didn't feel sorry for British captive Alan Henning, who was held by the extremist group.