The family of the murdered Harry Potter actor Robert Knox called yesterday for tougher action against teenagers carrying knives.

The 18-year-old was killed outside the Metro bar in Sidcup, southeast London, as he tried to protect his younger brother, Jamie, from a man armed with two knives.

The actor, who plays the Hogwarts student Marcus Belby in the forthcoming film Harry Potter and the Half-Blood Prince, was the ninth teenager to be stabbed to death in London this year.

He was a member of the same rugby club as Jimmy Mizen, who was stabbed to death two weeks ago at a bakery in Lee, southeast London.

The actor’s parents, Colin and Sally, and his brother visited the scene of the murder yesterday. Colin Knox, 55, who works in media production, said that the last conversation he had had with his son was on the danger of knives. “With knives there are no winners and only losers. If you are a person who carries a knife, think about the consequences before you carry the knife,” he said.

Mr Knox said that the recent wave of knife crime in the capital was a political issue and added: “There’s a lot of fear out there and basically someone has to change the way we think.”

Sally Knox, 50, a retail buyer, said: “I can’t understand personally the people who are against this stop-and- search because they think that it will make it worse.”

Jamie, 17, an Olympic hopeful in Tae Kwon Do, left a card at the murder scene which read: “I looked up to you so much. Everyone you met you touched. I would never have thought it would turn out this way. I thought you were invincible.”

Knox completed filming of the latest Harry Potter last Tuesday and had signed to appear in Harry Potter And The Deathly Hallows, the seventh film in the franchise. He had been acting since the age of 11 and had appeared in the 2004 film King Arthur, the BBC comedy After You've Gone, The Bill and Tonight with Trevor McDonald on ITV and the Channel 4 reality show Trust Me, I’m A Teenager. Karl Bishop, 21, from Chislehurst, southeast London, is being held in custody on suspicion of murder.

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