London - A 22-year-old British man was Thursday given a life sentence for stabbing to death a young actor who had a role in the next Harry Potter film.

Karl Bishop, who had a previous conviction for knife crime, murdered 18-year-old Robert Knox in a fight outside a bar in Sidcup, south London, last May.

The court heard that unemployed Bishop "habitually carried knives" and had a previous conviction for a knife attack.

He would have to serve at least 20 years in jail, the Old Bailey Criminal Court in London ruled.

Knox, a promising young actor, had just completed filming a part in Harry Potter And The Half-Blood Prince, in which he played the part of Marcus Belby, when the attack took place.

He was killed trying to protect his 17-year-old brother, Jamie, who had been threatened by Bishop, the court heard.

It emerged during the trial that Bishop was under police investigation for a knifepoint robbery and burglary, but had not been arrested.

Knox's parents said that while they could never forgive their son's killer, they would continue their campaign against youth knife and gun crime in Britain.