Three youths were each sentenced to 12 years in jail and a teenage girl was given eight years today for kicking David Morley, a bar manager, to death for fun and recording it on their mobile phones.

The Clockwork Orange-style gang hunted the streets of London’s South Bank, and targeted eight victims in five separate attacks during a "happy slapping" spree of random violence.

They were convicted at the Old Bailey last month of the manslaughter of Mr Morley, 38, a survivor of the nail bomb blast at the Admiral Duncan pub in Soho. They were acquitted of the more serious charge of murder.

Reece Sargeant, 21, Darren Case, 18, and David Blenman, 17, were each given 12-year sentences.

Chelsea O'Mahoney, who is now aged 16, was sentenced to eight years. She was said to have kicked Mr Morley’s head like a football as he lay on the ground. The pathologist’s report said that his injuries were similar to those of someone who had fallen from a great height.

Sentencing the four, the judge said: "No-one listening to this case could fail to have been affected by your selfishness and blindness to the suffering of others.

"You sought enjoyment from humiliation and pleasure from the infliction of pain, and you were clearly determined to continue and take advantage of any opportunity that presented itself.

"Each of your victims was totally innocent and taken totally by surprise. You behaved with total indifference to those who crossed your path in the heart of London. No citizen of this country should be in fear of or subjected to this sort of behaviour."

During their trial, it was alleged that the four mirrored the gang in the fictional book and film Clockwork Orange, seeking violence for violence's sake.

In Anthony Burgess’s portrayal, codewords were used to signal violence. The real life attacks were triggered with the words "You know what time it is" - signalling who would lead the violence and strike the first blow. It was described by the prosecution as "random, indiscriminate violence for what can only have been pleasure".

Mr Morley and his friend Alastair Whiteside had been chatting by the River Thames when they were both attacked by the grinning youths on October 30, 2004. Mr Whiteside saw his companion’s head being kicked.

After the killing, the gang carried on their attacks. Within one hour they had set upon eight people in what the judge described today as an "orgy" of five separate attacks. All took place along the South Bank theatre complex of the River Thames, around Waterloo and Hungerford Bridge.

Mirroring the notorious "happy slapping" craze, O’Mahoney filmed their final assault on a mobile phone.

Mr Morley, of Chiswick, west London, had already been a victim of an outrageous crime. On April 18, 1999, he had been working at the Admiral Duncan in Old Compton Street when it was bombed. "He survived that only to die in this," said Richard Horwell, prosecuting counsel.

In a local mark of respect, a project in the borough of Lambeth to tackle homophobic bullying by young people was named after Mr Morley, who was gay.

The defendants stood impassively in the dock while they were sentenced, but there were angry scenes in the public gallery as a relative shouted furiously before being led from the court by members of his family.

All the defendants are from Kennington, South London. The Common Serjeant of London, Brian Barker, lifted a court order today which had banned the identification of the younger two.

The judge added that the gang had been out on previous expeditions and had become obsessed with catching people unawares, assaulting them and filming it to laugh over later. He said: "You called this ‘happy slapping’ - no victim on the receiving end would dignify it with such a deceptive description."

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