London: A gunman was jailed for at least 28 years on Thursday for the murder of a former boxing champion who had asked a group of men to stop smoking in a bar.

Kanyanta Mulenga, 23, was given a life sentence at the Old Bailey after being found guilty of killing James Oyebola, 46, in Fulham, west London, in July 2007.

"This was nothing short of a brutal killing carried out for the most trivial of reasons," judge Peter Rook said, according to the Press Association.

Oyebola, who was shot in the neck and leg, died in hospital four days after the shooting when doctors switched off his life-support machine.

The father of three had been asking people to stop smoking in the garden area of the bar, which counted as enclosed premises because it had a retracting roof.

Police said Mulenga and his friends "sauntered away from the scene" after the shooting, with one of them grabbing a bottle of vodka from the bar on their way out.

"The defendant chose the cowardly option of pulling a gun on James over something as minor as smoking a cigarette," said Detective Inspector Steve Horsley, of the Metropolitan Police, who led the investigation."

A fourth man, who cannot be named for legal reasons, will face a separate trial.