Prime Minister David Cameron was preparing Thursday for a key vote on joining air strikes in Iraq as police arrested nine people, including a notorious radical preacher, accused of links to Islamist extremism.
Cameron was meeting ministers after returning from the UN General Assembly in New York, where he announced that parliament would vote Friday on British planes joining US-led strikes against the Islamic State (IS) group in Iraq.
With the prime minister set to argue that the jihadists pose a direct threat to Britain, nine people were arrested in London early Thursday on suspicion of encouraging terrorism and belonging to and supporting a banned organisation.
They are accused of being members of the extremist Islamist group Al-Muhajiroun, co-founded by one of the detained men, Anjem Choudary, the Press Association reported.
The arrests "are part of an ongoing investigation into Islamist-related terrorism and are not in response to any immediate public safety risk," Scotland Yard said.
Police are also searching 19 properties following the arrests, all but one in London.
Al-Muhajiroun aims to overthrow the British government and replace it with an Islamic state before establishing a global Islamic caliphate, according to the London-based International Centre for the Study of Radicalisation and Political Violence.
US planes, joined last week by French fighter jets, have been launching strikes on IS targets since early August after the jihadists seized swathes of land in Iraq and Syria.
Dutch fighter jets are also set to join in the strikes.
Islamic State fighters have beheaded a British aid worker and two US journalists, while an organisation linked to IS has also executed a French tourist in Algeria.
IS is also holding two other Britons.
While securing British support may not be crucial to the US-led offensive, Cameron told the UN Security Council he wanted it to "play its part" after US President Barack Obama urged the global community to unite against a "network of death".
- Spectre of 2003 Iraq war -
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"Arguably the UK is not needed because the US has the capability, other nations, France included are involved," said Afzal Ashraf, a consultant fellow at defence think-tank the Royal United Services Institute.
"But it isn't a question of whether the UK is needed, it's a question of whether the UK feels it has a responsibility."
Cameron has taken a cautious approach to military action against Iraq, haunted by a damaging House of Commons defeat over military action against President Bashar al-Assad's regime in Syria last year.
Although he has ruled out sending in ground forces, many lawmakers are also likely to be cautious about air strikes on Iraq as Britain's involvement in the 2003 US-led invasion of the country remains deeply unpopular.
A total of 179 British personnel died in Iraq between 2003 and 2009.
Cameron has warned them not to be "so frozen with fear" by past events "that we don't do anything at all."
Although Cameron could face some hard questions during Friday's debate, the main opposition Labour party and his coalition partners the Liberal Democrats have pledged to support him in the vote.
Hundreds of anti-war protesters are expected to protest outside Downing Street later Thursday against the action.
Officials believe that around 500 Britons have travelled to fight alongside IS jihadists and British media reported Thursday that up to five British passport holders have been killed by air strikes in Syria.
The mother of one, 19-year-old Ibrahim Kamara -- known in Syria as Khalil al-Britani -- said she had learnt of her son's death this week through social media.
Khadijah Kamara added that she knew he was going to die when she discovered where he was.
"I cried then. What's left to cry now? He's gone. I have three other boys, I have to be strong for them," she told the Guardian newspaper.