Gabriel Stoyanov, 21, was attacked by the youths after getting off the 181 service in Bromley, southeast London, late on 4 November last year.

The business management undergraduate had been out drinking with a friend and, after they got on the bus, he attempted to engage with the defendants, now aged 15, 17 and 18.

The defendants, who later claimed they had acted "in self-defence", got off the bus two stops later and went to the home of the 17-year-old.

They armed themselves with weapons and lay in wait for the victim outside a takeaway restaurant, the court heard during the teenagers' sentencing on Friday at the Old Bailey in London.

CCTV showed Mr Stoyanov come out and back away as he saw the defendants.

Alfie Kibble, 18, swung a motorcycle chain at him - but missed - and the 15-year-old lobbed a bottle before the 17-year-old stabbed the victim in the chest with a knife.

The 15-year-old and 17-year-old boys cannot be named for legal reasons.

The teenagers ran away and Mr Stoyanov was rushed to hospital, where he died the next day.

Judge John Hillen said the motive, "as incredible as it seems", was that they were annoyed at the victim's "boorish behaviour on a bus".

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Prosecutor Edward Brown KC told jurors: "He was killed for being little more than drunk and annoying, perhaps very annoying.

"However, nothing he did reasonably justified, in law or otherwise, being attacked and killed."

The 17-year-old boy was found guilty of murder and given a life sentence with a minimum term of 15 years.

Kibble, from Bexley, southeast London, was found guilty of murder and jailed for life with a minimum term of 14 years and nine months.

The 15-year-old, who "lured" the victim towards his more heavily armed friends, was given a sentence of six years and eight months for manslaughter.

The defendants were also convicted of being in possession of offensive weapons which was reflected in their sentences.

Judge Hillen said Mr Stoyanov had been described by his loved ones as "easy going, compassionate and always ready to help others".

"He is described by his mother as being full of life and dreams and energy to achieve them," he added.

"He had a sparkling personality and infinite goodness in his spirit. He was the joy of his family and his untimely death has devastated them."