A violent thug who launched three separate unprovoked attacks while out of his head on a legal high has been jailed for 12 years.

And Lewis Morrison will have to serve two thirds of that time behind bars before he can seek parole and then he will be on licence for an extra four years.

A judge at Swindon Crown Court heard how the 21-year-old stabbed one man in a Trowbridge street, savagely beat another on his own doorstep and set about a third at work.

Rob Welling, prosecuting, said the first attack took place at Chippenham College on Wednesday November 4 last year.

He said an IT technician was leaving the campus after a day's work when he was aware of shouting in the car park.

Morrison then aggressively brushed past him, as if looking for fight, as the worker retreated to the foyer where a facilities manager spoke to the defendant.

There was then a melee where Morrison threw a number of punches and kicked out at the men before the police arrived and arrested him.

He was on bail when he launched the second attack on a vulnerable man on Union Street in Trowbridge on Thursday February 25.

Mr Welling said the victim, who is an alcoholic and has a brain injury, was sitting on a bench when Morrison approached and demanded money from him.

After going through his pockets and taking cash and tobacco at knifepoint he stabbed the victim in the lower back.

The last incident took place the following day when he knocked on the door of a man who vaguely knew.

When the victim answered, who was waiting for a pizza to be delivered, answered just after 9pm Morrison asked if the house was number 43, which was nearby.

He then launched a sustained attack, raining numerous punches on the victim leaving him with a badly broken jaw and smashed tooth.

As a result of the beating the victim had to undergo surgery to have a metal plate inserted in his jaw, which was also wired.

The defendant was arrested soon after when he was found hiding in his house but was not questioned as officers feared for their safety.

Morrison, of no fixed abode but formerly of Charlotte Square, Trowbridge, admitted wounding with intent to cause grievous bodily harm, grievous bodily harm with intent, robbery, having an offensive weapon, two common assaults and theft.

Tony Bignall, defending, said his client, who had ADHD, started smoking cannabis when he was just 11 years old before moving on to legal highs.

"After his last prison sentence he started smoking something called Spice. He found on his release he became dependant on Spice," he said.

When he tried to come off the drug it had led to psychosis, he said, and led to him trying to jump out of a third storey window.

Jailing him Judge Simon Carr said "You fall to be sentence for a terrible series of violent attacks on what were complete strangers.

"The only explanation you can come up with is you believe your behaviour was caused or exacerbated by the use of legal highs.