Police have used a Taser stun gun on a man armed with two knives outside Buckingham Palace in central London.
Officers discharged the weapon when the man, thought to be in his 50s, acted aggressively when challenged outside the centre gates at 11:50 GMT.
The Metropolitan Police said he was arrested on suspicion of causing an affray.
Two knives and a pair of trainers were left inside a police cordon set up around the area.
Changing the Guard
The Queen and Prince Philip were at Sandringham at the time.
A spokesman for the Met said: "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."
The man was spotted with the weapons during the Changing the Guard ceremony.
Buckingham Palace said it would not comment on what was a matter for the police.