A suspect deliberately drove a car at police outside Buckingham Palace and then "reached for a 4ft sword", the Metropolitan Police have said.
Three officers were injured after tackling a man who drove a blue Toyota Prius at a marked police vehicle on Friday night.
Commander Dean Haydon, of the Metropolitan Police counter-terrorism branch, said: "Uniformed officers then confronted the driver of the vehicle and during that confrontation the driver reached for a four-foot sword that was in the passenger footwell.
"CS gas was used as part of the arrest and during the struggle the individual repeatedly shouted the words Allahu Akbar."
A 26-year-old man from the Luton area is in custody at a central London police station.
Mr Haydon praised the bravery and courage of the injured officers in "quickly bringing the incident under control".
He also said he was "confident" that it was an "isolated incident".
— Rach King (@rachking93) August 25, 2017