A 20-year-old man from south east London was today arrested on suspicion of terrorism offences.
Counter-terror police held the man from Thamesmead for questioning over allegations that he was preparing for a terrorist act, Scotland Yard said.
He was taken to a south-London police station where he remained in custody this afternoon.
The arrest was made under the Police and Criminal Evidence Act.
The move is one of a wave of terrorism arrests across London and the rest of the country since the terror threat level in the UK was raised from substantial to severe.
The Joint Terrorism Analysis Centre raised the threat level in August against a backdrop of increasing concerns over hundreds of aspiring British jihadis travelling to Iraq and Syria to learn terrorist "tradecraft".
Fears of a terrorist attack on Britain's streets have heightened in the wake of the rise of Islamic State (IS), the extremist group that has taken over large swathes of Iraq and Syria and attracted thousands of foreign jihadists to its cause, including more than 500 Britons.
A new Counter-terrorism and Security Bill, containing a range of draconian powers including new orders that can block suspected British fighters from returning to the UK, was introduced to Parliament last month.
