Controversial Respect MP George Galloway was badly bruised after he was attacked in the street tonight, his spokesman said.
Mr Galloway was posing for pictures with people in Notting Hill, west London, when the incident happened.
The spokesman said: "George was posing for pictures with people and this guy just attacked him, leapt on him and started punching him.
"It appears to be connected with his comments about Israel because the guy was shouting about the Holocaust.
"George is badly bruised but OK. He has bruising to his head and face and is in a pretty bad shape."
Metropolitan Police said a man had been arrested on suspicion of ABH and taken to the south London police station where he remains.
The motivation for the attack is unclear but Mr Galloway caused recent offence when he announced Bradford was an "Israeli-free area".