A motorist slammed into pedestrians and cyclists near Britain's Houses of Parliament on Tuesday and police are treating the incident as an act of terror.
A terror suspect is believed to have travelled through the night from Birmingham to stake out Westminster for more than an hour and a half before mowing down cyclists outside the Houses of Parliament.
The 29-year-old man, believed to be of Sudanese origin, waited until the morning rush hour local time before swerving on to the wrong side of the road and hitting cyclists who were waiting at traffic lights, then crashed into barriers outside the entrance to the House of Lords.
The man, who has British nationality, had driven from his home in Birmingham, sparking suggestions that it was an attempted "copycat" attack to that perpetrated by Khalid Masood a year earlier which killed six people.
Masood had lived just 10 minutes from the suspect's home in the Sparkbrook area of Birmingham.
Security services will be keen to establish whether there are any connections between the pair.
Three cyclists were injured in the attack. The two who required hospital treatment had been released today.
It was suggested that the attacker, who was known to have been in Westminster since 6am local time, may have been on a reconnaissance mission and was spooked into taking immediate action at 7.37am when an ambulance pulled up behind him with sirens blazing.
Scotland Yard said that the man was not known to counter-terror police or MI5, but sources suggested that he was known to West Midlands Police.
Officers were last night facing questions over a white van that was seen behind the man's Ford Fiesta and filmed following it on to the wrong side of the road before stopping near the point where it crashed into barriers. Another van was also seen stopping on the wrong side of the road in the seconds after the crash.
Both police and security sources insisted that the driver was not being followed, but confirmed that an unmarked police van was in the area on unrelated matters and stopped after the crash. They did not confirm which van belonged to them.
Bicycles are placed against a wall near the scene outside the Houses of Parliament in London.
The Government made an apparent defence of the security services by releasing figures showing there has been a huge rise in suspected terror plots, with live investigations rising from "more than 500" in March to 676 by the end of June.
In a statement from her holiday in Switzerland, Theresa May said: "For the second time in as many years the home of our democracy, which is a potent symbol of our precious values of tolerance and freedom, has witnessed terrible scenes just yards from its door.
"The threat to the United Kingdom from terrorism remains severe. I would urge the public to remain vigilant, but also to come together and carry on as normal."
Sajid Javid, the Home Secretary, thanked police for their response and was returning to London from a family break.
Reacting to the attack, US President Donald Trump said on Twitter: "These animals are crazy and must be dealt with through toughness and strength!"
Scotland Yard was questioning the man on suspicion of terrorism offences.
A forensics officer works near the scene near of a car that crashed into security barriers.
Officers were piecing together his movements, revealing that he spent several hours in Soho before travelling to Westminster. Sources say that he is then believed to have staked out potential targets before launching his attack.
Chris Phillips, former head of the National Counter Terrorism Security Office, said the attack seemed to be a "very poor copycat" of Masood's attack on March 22 last year and pointed out police found no weapons in the car.
The suspect's home is a short drive from Edgbaston, where Masood was living when he took a rented car to Westminster and mowed down five people before jumping out and stabbing constable Keith Palmer to death. Masood was shot by police.
The Ford Fiesta used in yesterday's attack was first registered in Nottingham in 2010 but had changed hands just two months ago, records show.
Police raided two addresses in Birmingham and one in Nottingham. The landlord of one of the flats being searched in Sparkbrook said that the suspect, named locally as Salah, had lived there until four months ago.
Regulars at a nearby Sudanese coffee shop recognised the attacker and described him as a "normal, quiet man" who would frequently drop in. "I think the last time I saw him was last week," said a local barber, who did not want to be named.
Around eight plain clothes police officers appeared to be involved in the search of a three-storey house in Radford, Nottingham.
Several left in a silver car, some carrying documents.
