The sister of murdered schoolboy Alan Cartwright has called for more stop and searches after his knife-wielding killer was jailed for a minimum 21 years.

It comes after the Metropolitan Police said knife crime is up 18 per cent in London this year. Meanwhile, stop and searches have been downscaled since 2011 after overuse by officers.

But Dean Haydon, head of Scotland Yard’s homicide and major crime command, said that as a result of this, the deterrence to carry a knife “is less”.

On Friday, Joshua Williams, 18, was sentenced after a jury found him guilty of Alan’s murder. He stabbed the 15-year-old in the chest as he cycled in Caledonian Road on February 27.

The Old Bailey heard that at the time of the attack, Williams was on bail on suspicion of carrying a four-inch long lock blade.

And speaking to the Gazette on Monday, Alan’s sister, Cherrie Smith, said: “Had Joshua Williams been stopped and searched, maybe my brother would still be alive.

“Potentially stop and searches would deter people from carrying knives. I appreciate it is a sensitive issue, but if you have nothing to hide, you have nothing to hide.”

Alan is one of 10 youngsters to have been stabbed to death in the capital this year.

He is also one of two victims in Islington, after 18-year-old Stefan Appleton was killed at Nightingale Park in Canonbury on June 10. Six 16-year-old boys were arrested in connection with his killing.

Ms Smith, 22, said she was at a loss as to understand how young people get involved in such violence: “I feel like somewhere along the line, between primary school and secondary school, there is some sort of void that sucks children or teenagers into this life. I’m trying to work out what goes on in that period.

“They all go to school or college. Maybe they are not afraid to cross the line set by schools, parents and police. I know that Al or I would never dare cross that line with our parents. But at the same time, some kids tend to grow up so quickly so it’s difficult.”