A man has been arrested on suspicion of terrorism offences after a car crashed outside the Houses of Parliament.
One woman is being treated in hospital for serious but not life-threatening injuries, Scotland Yard said. Two others were also injured.
The man in his late 20s was held after the crash, shortly after 07:30 BST. He is not believed to be known to police.
Counter-terrorism police said the suspect was not cooperating and has not been formally identified.
Scotland Yard’s head of counter terrorism Neil Basu said there was “no intelligence at this time of further danger” to London or the UK as a whole.
The man is in custody at a south London police station and the vehicle is being searched. The government’s Cobra emergency committee is meeting later.
No one else was in the car and no weapons have been found so far. The Met’s Counter Terrorism Command is leading the investigation.
A number of eyewitnesses have said the silver Ford Fiesta, which was travelling westbound, appeared to deliberately hit cyclists and pedestrians as it swerved into the opposite lane.
Footage released by the BBC shows the moment when the car drives over a pedestrian crossing before crashing into the security barriers.
Images posted to social media showed a man in handcuffs being led away from the car by officers after the crash.
BBC News home affairs correspondent June Kelly described the terror arrest as a “significant development”.
“The police will be looking at this man’s background, his identity – they’ll either know it or they will be working towards it,” she said. “They will be looking at his beliefs his associates, also his mental state.