Police used a taser gun on a man seen pointing a knife at his own throat outside the British prime minister's Downing Street residence, police said on Monday.
The 42-year-old man, who had been shouting in the street, failed to respond when challenged by police shortly before 9:00 pm on Sunday, and was then hit with the electric weapon.
He suffered a minor head injury when he fell and was taken to hospital as a precaution.
He was later arrested on suspicion of possession of a knife and affray, and remained in custody Monday.
The prime minister's apartment and office is at 10 Downing Street, a road now sealed off by high gates at both ends.
The incident came exactly a month to the day since police used a Taser on a man brandishing knives outside Buckingham Palace, the sovereign's official residence.
Talhat Rehman, 54, was charged with affray and possessing a bladed weapon in public.