07/10/2014 17:03 BST | Updated 07/10/2014 17:59 BST

Four Suspected Islamists Terrorists Arrested In Raids Across London

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Armed police patrol streets around New Scotland Yard after terrorist bombings London 7 July 2005 UK. (Photo by Photofusion/Universal Images Group via Getty Images)

Four suspected Islamist terrorists have been arrested in a series of raids across London. One of the suspects - aged 21 - was tasered during his arrest but was not injured and did not require medical treatment, Scotland Yard said. Counter terror police arrested the men - two aged 20 and two aged 21 - and were helped at one address by armed officers, although no shots were fired.

It is understood at least one of the suspects is believed to have travelled to Syria. A Whitehall source told the Press Association that officers believe the raids were an "early disruption" of what could have been a "significant plot". A Scotland Yard statement said: "These arrests and searches are part of an ongoing investigation into Islamist-related terrorism."

All men were arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism and have been taken to police stations in central London and remain in custody. A number of residential addresses and vehicles are being searched by specialist officers in west and central London as part of the investigation.

bernard hoganhowe

Hogan-Howe: 'The drum beat beat around terrorism has changed'

Commenting on the arrests, Metropolitan Police Commissioner Sir Bernard Hogan-Howe told BBC London Radio: "It is difficult to talk in a great deal of detail about it, but it is a quite serious case. It is one of a series of arrests that we have had over the last few weeks which taken together for me confirm that the drum beat beat around terrorism has changed.

"It's a more intense drumbeat - we are having to be more interventionist and a lot of it is linked back to Syria and Iraq. These are arrests that in some way or other have got that sort of link. I don't want to worry the people of London - we are here to keep them safe and we believe we are on top of things - but there are some concerns about the people we are having to arrest."