The 42-year-old was challenged by police just before 9pm yesterday but failed to respond so the electronic weapon was used.
The man had been shouting in the road and appeared to have a knife that he was pointing at his throat.
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 remains in custody.
Two police officers from the Diplomatic Protection Group fired the Taser.
It follows a separate incident last month when police outside Buckingham Palace used a Taser on another man who was also accused of brandishing a knife.
More top news
Two police officers helping to guard diplomats have been sacked for sharing pornographic images on their mobile phones.
A 32-year old man from Hampton has been jailed for five years historic sexual assaults in the late 1990s.
A teenager who was mistakenly released from prison after he was arrested on suspicion of attempted murder has been detained by police.