Evren Anil, 23, died after being punched in the face when he remonstrated with them over a half-eaten Lion bar one of them had thrown into the car he was in.

Dejon Thompson, 16, and Patrick Rowe, 17, admitted manslaughter and knife possession at a hearing last month.

Judge Ann Goddard lifted restrictions banning the pair being identified and condemned their "yobbish and stupid behaviour".

Members of the victim's family complained that the elder of the two youths had made gun gestures with his hand towards them at the previous hearing.

Elif Anil, 26, the victim's sister, who was with him at the time, said it was a "vicious and callous attack" and branded the killers "heartless cowards".

Prosecutor Joanna Korner QC told the Old Bailey Mr Anil and his sister were waiting at traffic lights in her Peugeot 307 in Gipsy Hill, south east London, when the older of the youths threw a half-chewed Lion bar through the car's open window.

Mr Anil got out of the vehicle and threw it back at them, only for one of the boys to produce a 4in knife from his trousers.

As his sister screamed, a knife was held to his throat and he was then punched in the face so hard that his skull was fractured, and he suffered a haemorrhage. He died of severe head injuries eight days later.

Rowe, of Cumberton Road, Tottenham, north London, admitted throwing the chocolate bar and delivering the fatal blow to Mr Anil. It was he who carried the knife to the scene and gave it to Thompson, of Langdale Road, Thornton Heath, London, who threatened the victim.