Six men have been arrested in anti-terror dawn raids across London and Luton.
They are believed to include Abu Izzadeen, also known as Omar Brooks, who made headlines when he heckled Home Secretary John Reid at an event last year.
The men are suspected of "inciting others to commit acts of terrorism overseas and terrorist fundraising", a Met police spokesman said.
The Met's Counter Terrorism officers swooped on five addresses in the capital and one in Luton, Bedfordshire.
Searches are ongoing.
The arrests form part of a long-term investigation into radicalisation and funding of international terrorists, Scotland Yard said.
All six suspects are being questioned at a high-security police station in London.
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