Eyewitness Grant Shepherd has filmed the moment a man wielding two knives was Tasered outside Buckingham Palace.
The man is seen falling to the ground before being detained, while officers on horseback keep the crowds of tourists back.
Pictures from Grant Shepherd
Kevin Burrows witnessed a man being Tasered by police outside Buckingham Palace earlier today. He described the incident to ITV News' Reporter Damon Green:
A spokesman for the Metropolitan Police said:
It was approximately 11.50. A man was seen outside the centre gate in possession of two knives.
He was not making threats to members of the public but he was challenged by police.
He acted aggressively and a Taser was discharged.
He is thought to be in his fifties. He was arrested on suspicion of affray and has been taken to a central London police station.
An eyewitness to the arrest at Buckingham Palace told me that police walked behind the suspect and Tasered him in the back.
A scene was cordoned off with police tape 30 metres from the palace gates this morning and an ambulance was parked to the side of the building.
Inside the cordoned-off area lay two knives with six-inch blades and a pair of Nike high top trainers.
Taser wire also lay on the floor with four plastic tubes of two different sizes, three large ones and a small one.
A hat and a black carrier bag containing paper material with a handkerchief beside it also lay on the ground.
The man's face has been blurred for legal reasons.
The Queen and Prince Philip were at Sandringham at the time of the incident.
A Buckingham Palace spokeswoman said they would not comment as it was a police matter.
A man has been Tasered by police outside Buckingham Palace, Scotland Yard said today.
A Metropolitan Police spokesman said the incident took place at 11.55am but they did not have any further information.
A man was charged today with killing another man in a nightclub.
Ashley Milne, 22, of Peckham, south east London is accused of the murder of Jamie Sanderson, 20, at the Oceana nightclub in Clarence Street, Kingston, south west London, Scotland Yard said.
He will appear in custody at South Western Magistrates' Court on Monday.