Robert collapsed near the town hall

The Old Bailey heard the boy, who cannot be named because of his age, stabbed Robert Levy, 16, in Hackney, east London, last September.

Judge John Diehl warned the youth he would be detained and remanded him in custody for sentencing next month.

Robert's family described him as a "hero who tried to save someone".

Sasha Wass QC, prosecuting, said: "He happened to have just come out of his house when the trouble started.

"That trouble resulted in his death.

Law book

"Robert saw the defendant produce a knife and one witness heard him (Robert) say: 'You can't do that' and then the defendant stabbed Robert three times."

Robert was stabbed three times, once in the neck severing an artery which caused his death before he reached hospital, and also in the stomach and shoulder.

Miss Wass said Robert ran off after being wounded and collapsed near Hackney Town Hall.

The youth claimed he acted in self-defence and that he had been terrorised by a gang to which the boy he was confronting belonged.

When police searched his home, they found a law book in the loft with pages on self-defence photocopied from it.