Three police forces were involved in raids in Birmingham and Nottingham on Tuesday afternoon following the arrest of a 29-year-old British man on suspicion of terror offences.
Armed officers had swarmed Westminster at about 7.40am on Tuesday, when a silver Ford Fiesta ploughed into cyclists and pedestrians outside parliament before being halted by security barriers.
Images posted to social media showed a man, wearing a black puffer jacket and surrounded by officers, being led away in handcuffs from the hatchback. Detectives said later on Tuesday they believed the car had been driven to London from Birmingham overnight.
The Fiesta was spotted in the Tottenham Court Road area at 1.25am, the Metropolitan Police said, where it remained until about 6am. It was then driven to Westminster.
“There was not a police car in pursuit of the vehicle” when it crashed, Neil Basu, the Met’s head of counter-terrorism, told reporters.
Three people were hurt in the crash, one seriously.
Theresa May said that terrorists would “never succeed” in dividing the UK, after Donald Trump blamed “crazy animals” for the attack in a tweet.
The crash was an “appalling incident”, the prime minister said, adding that the terror threat facing the country remained “severe”, meaning another attack was highly likely.
See below how we covered developments in this story
A man has been arrested after a car crashed into barriers outside the Houses of Parliament. Streets around Parliament Square, Millbank and Victoria Tower Gardens have been cordoned off as dozens of armed police swarmed on the scene. Armed officers could be seen surrounding the car before leading a man away in handcuffs. A series of ambulances arrived at the scene.
The Houses of Parliament are surrounded with security barriers of steel and concrete.
The measures were extended in the wake of the Westminster Bridge attack in March 2017, when Khalid Masood ploughed a car into crowds on Westminster Bridge, killing four people.
Masood abandoned his car then stabbed and killed unarmed Pc Keith Palmer before he was shot by armed police in a courtyard outside Parliament.
Eyewitness Ewalina Ochab told the Press Association: "I think it looked intentional - the car drove at speed and towards the barriers."
She said: "I was walking on the other side [of the road]. I heard some noise and someone screamed. I turned around and I saw a silver car driving very fast close to the railings, maybe even on the pavement."
"The person driving did not go out" of the vehicle, she said.
The vehicle did not appear to have a front registration plate when it crashed, she added.
Our Home Affairs Correspondent, Lizzie Dearden, reports from the scene:
Westminster Tube station has now been shut down and police are clearing out hundreds of commuters after widening cordons around the scene.
A helicopter is circling ahead as armed police guard cordons shutting off a large area of Parliament Square, Whitehall and the end of Westminster Bridge.
Police say the cordons could be made bigger still and are asking people to move further back.
Ashley Cowburn, our Political Correspondent, who was in the Houses of Parliament at the time of the crash, writes:
The Houses of Parliament are currently in lockdown following the incident meaning there is no access to the building or exit for those currently inside.
The Commons is currently in the middle of the summer recess and the large majority of MPs, peers and staff are away from the estate.
Members of the public and press have been moved back further from the area as police put up a "Terrorism Act cordon", according to an officer at the scene.
The cordon has been extended past the Cenotaph on Whitehall - a five-minute walk from the scene at Old Palace Yard.
Police are also ordering pedestrians to move south of Westminster Bridge.
