Mr Whelan was stabbed to death on the top deck of a bus

Anthony Joseph, 22, denies murdering Richard Whelan, 28, who was stabbed seven times on a bus in Holloway Road, north London, in July 2005.

Mr Whelan intervened when the accused began throwing chips at his partner Kerry Barker, 38, the Old Bailey heard.

Mr Joseph, of Islington, denies murder and is being retried after a previous jury failed to reach a verdict in May.

Victor Temple QC, prosecuting, said the re-trial centred on Mr Joseph's mental health at the time of the murder.

The defence alleged their client was suffering from the onset of schizophrenia.

Mr Joseph's lawyer Philip Katz QC said his client should be found guilty of manslaughter on the grounds of diminished responsibility.

Drink and drugs

Mr Whelan had been travelling on the number 43 bus with his girlfriend Kerry Barker, the court was told.

Mr Joseph began throwing chips at an American woman as she spoke to her husband on her mobile.

Mr Temple said: "She said he had a distinguishable smile or smirk on his face and he seemed really weird."

Ms Barker said Mr Joseph then began throwing chips at her and one hit the back of her head.

Mr Temple said: "Mr Whelan was not prepared to sit down and do nothing. He got up and approached the defendant.

"An altercation broke out which was between equals. The defendant who habitually carried a knife, became verbally and physically aggressive."

Mr Joseph is alleged to have produced a knife and stabbed the unarmed Mr Whelan in the top part of his body up to seven times.

"The defendant had been drinking and taking drugs and needed little or no excuse to turn his pent up anger against the innocent victim," said Mr Temple.

The trial continues.