A 21 year old man was tasered when four suspected Islamist terrorists were arrested in a series of raids across London, but did not require medical attention.
The Scotland Yard officer said, counter terror police arrested the men - aged between 20 and 21 - and at one address were helped by armed officers but no shots were fired.
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.