A suspected jihadist armed with several knives was thought to be heading towards Downing Street when he was dramatically arrested by armed police, security sources have revealed.
The 27-year-old man was carrying a rucksack containing at least three knives when he was detained “following a stop and search as part of an ongoing operation”, police said.
The ‘lone wolf’ suspect had been under close surveillance when counter-terrorism officers ordered his immediate detention as he came within 300 yards of the gates of the Prime Minister’s residence.
It is understood that the suspect’s family had become concerned about his behaviour and reported him to the authorities several weeks ago. Investigators believe he was about to launch an attack.
The 27-year-old man, dressed head to toe in black, was wrestled to the ground by armed police officers as he walked among a crowd of tourists and workers in Parliament Street at just after 2.20pm yesterday.
His arrest came just five weeks – and a 100 yards away – from the spot where Khalid Masood was shot and killed within the grounds of the Palace of Westminster, having mowed down bystanders in a hired car driven over Westminster Bridge.
The Telegraph understands that the man, who is understood to have been born overseas but who lives in south east London, was known to the security services and was being watched as part of an ongoing counter-terrorism operation.
Images from the scene showed three knives and what appeared to be a mobile on the ground close to a brown rucksack.
An officer in forensic overalls could be seen taking photographs of the knives.
The suspect was detained at the scene for several minutes within view of journalists and passers by before he was eventually taken away in a police vehicle.
Recruiters Harry Peasnell, 27, and Andy Burnage, 22, were leaving the adjacent building which houses various Government offices after a meeting with officials when they were told over the tannoy the usual entrance on to Whitehall was closed.
As they made their way back towards Parliament from the alternative House Guards Road entrance they said they were pushed back up Great George Street by several plain clothes police officers.
They then made their way to Parliament Square where they said they saw a man in his 20s or 30s, who they thought was the suspect, being spoken to by police next to the wall of the offices.
Mr Peasnell, who says he regularly has meetings in Westminster, said police were quick on the scene and that he was not worried like he was during the terror attack in the area just weeks ago.
Last time all the buildings were on lockdown and no one was allowed to leave, he said.
Westminster has been on a state of heightened alert since Masood launched his attack on March 22, killing five people, including Pc Keith Palmer.
Scotland Yard said there were no reports of any injuries.