George Galloway was left dazed and bruised yesterday after being pelted with a rubber stress ball while out campaigning.
The firebrand Respect Party MP was on an open-top bus in central London when the ball was thrown from a nearby office block.
His aide, Kevin Ovenden, said: "It hit George on the left side of his head, on the temple.
"He was momentarily dazed and because of the impact of the blow he lost his balance and hit the other side of his head on the side of the bus.
"There is a nasty bruise on the side of George's head, but he will continue campaigning for the local elections."
The missile - described as slightly smaller than a tennis ball and hollow - is believed to have been flung from the first floor of an office block on Procter Street, Holborn, shortly after 2pm.
A 32-year-old man was arrested and later cautioned by police. He is believed to work at a research company.
Mr Galloway, 53, MP for Bethnal Green and Bow, received medical treatment but was not taken to hospital.
George Galloway left dazed and bruised as he's hit by rubber stress ball while on his election battle bus | the Daily Mail