A gunman faces life imprisonment for the “particularly senseless” murder of a former British boxing champion who had asked a group of men to stop smoking in a bar.

Kanyanta Mulenga, 23, was found guilty of shooting James Oyebola through the back of the neck three weeks after the ban on smoking in enclosed public places came into force in July 2007.

Mr Oyebola, 46, was drinking at the Chateau 6 bar in Fulham Broadway, southwest London, where he was a friend of the owner, when trouble began. Many of the 50 others present dived for cover or fled as Mulenga opened fire with a Baikal automatic pistol that he had smuggled past security in his waistband.

Mr Oyebola, who was hit in the leg and the neck, died four days later in Charing Cross hospital, having never regained consciousness.

Jeremy Donne, QC, for the prosecution, told a jury at the Old Bailey: “The reason for the killing was particularly senseless. James Oyebola had become involved in a dispute over smoking inside the club.”

Mr Oyebola, a former British heavyweight title holder who won a bronze medal in the 1986 Commonwealth Games, had been asking people in a “perfectly pleasant way” to put out their cigarettes in the garden area of the bar, which counted as enclosed because it had a retracting roof.

A witness described how the 6ft 9in father of three was jostled by three men. “He saw the victim standing just the other side of the glass doors, inside the garden, being jostled by three men. He thought it looked like a giant against kids,” Mr Donne said.

Rene McKoy, 20, of Battersea, and Dean Francis, 24, of Wandsworth, both in southwest London, who were in the bar with Mulenga, were cleared of murder after agreeing to give evidence for the prosecution.

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

Mulenga, of Putney, southwest London, hung his head as the verdict was read out, while his girlfriend had to be escorted from the public gallery after she interrupted proceedings by shouting: “What about my daughter?”

In a victim impact statement, Mr Oyebola’s partner Malin Bergstrom said: “The sudden and brutal death of my partner James has had a huge impact not only on me and my children but his family and friends. James was warm, kind-hearted and a generous person. He was by no means perfect but he had a genuine wish to better himself.”

The court heard that Mulenga was jailed for 30 months in September 2005 for possessing heroin and crack with intent to supply. He also had convictions for handling stolen goods and possession of cannabis.

Judge Peter Rook told Mulenga that he faced life imprisonment for the murder. He was remanded in custody to be sentenced today.

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