A 14-year-old boy became the youngest victim of the growing knife crime crisis enveloping London when he died from stab wounds after an argument with a group of youths.

David Idowu, who is the nineteenth teenager to suffer a violent death in the capital this year, is believed to have been stabbed in the stomach and chest.

He was attacked in Southwark, southeast London, three weeks ago and died from his injuries yesterday morning at the Royal London Hospital.

His death came as ministers promised a full review of how knife crime is prosecuted and how sentences are handed out by the courts amid growing public alarm at the extent of knife offending on the streets.

Jack Straw, the Justice Secretary, has admitted that he is powerless to stop new guidance coming into force next month under which some knife crime offenders could be given a fine.

Witnesses to the attack in Southwark said that the argument may have spilled over from a nearby football pitch. David was found critically injured behind student halls of residence on Great Dover Street. He was given first aid by staff at the Sidney Webb House, which houses 700 students from King’s College London, before being taken to hospital.

Devon Hanson, principal of Walworth Academy where David was studying, said that pupils and staff were shocked. “This is a terrible and unnecessary tragedy, and the whole school is deeply saddened. Our thoughts and condolences go to David’s family and friends.”

Detective Inspector Bernie Galopin, from Southwark CID, said: “Nearly three weeks after the attack on David he has lost his life, and this will now be a murder investigation. In light of David’s death, our immediate thoughts are with his family and friends. I would like to take this opportunity to appeal to anyone who has information, or who witnessed the attack but has yet to contact the police, to come forward.”

The investigation will now be handed over to officers from the Homicide and Serious Crime Command. A 16-year-old boy has appeared at Camberwell Youth Court accused of attempted murder.

Other teenagers to have suffered violent deaths in London this year have been aged between 14 and 19. Last year 26 teenagers were killed. The Ministry of Justice announced a review of the position on sentencing last night.

Under the rules, issued by the Sentencing Guidelines Council, magistrates have been advised that the starting penalty for carrying a blade in public should be a fine.

Tony McNulty, the Police Minister, attacked the new guidelines, which come into force on August 4. After admitting that he could not prevent their implementation, Mr Straw at first promised a review of the guidance, but then his department appeared to backtrack, saying that it was unaware of any such initiative.

Seven hours after Mr Straw made his comment at a press conference, and after officials had listened to a tape recording of his remarks, the Justice Department announced a “stocktake” of its position on knife crime. The new guidelines include a doubling of the maximum sentence for knife crime from two to four years and a presumption that anyone over the age of 16 caught with a knife in a public place will be prosecuted.

Paul Stephenson, Deputy Metropolitan Police Commissioner, said last week that tackling knife crime was now his force’s number one priority. He announced the creation of a 75-strong knife crime unit to target “known gang members and their associates”.

It was an admission that several weeks of high-profile stop-and-search operations had not apparently discouraged young people from carrying weapons.

David Cameron, the Conservative leader, said yesterday that anyone convicted of knife crime should expect a jail sentence.

Speaking at the launch of his party’s campaign in the Glasgow East by-election, he spelled out a hard line on knife crime. “We are proposing that anyone convicted of knife crime should expect to go to jail,” he said. “I don’t believe that the Government’s ‘presumption to prosecute’ is enough. It doesn’t send a strong enough signal. We need a ‘presumption to prison’.”

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