More than a quarter of London secondaries have taken up an offer of free knife detecting “wands”, Tes has learned.

The news comes as a wave of violent crime in the capital continues to grow, and as Ofsted revealed that it had begun an investigation into the problem. 

Last night, five more teenagers were stabbed on the streets of London, including a 13-year-old boy.

So far this year, a total of 11 teenagers have been fatally stabbed in the city, which, for the first time ever, has suffered a higher murder rate than New York, figures show.

Mayor of London Sadiq Khan has described an “epidemic” of knife crime and last June offered free metal detecting “wands” to all 498 secondary school and 63 FE colleges in London.

Latest figures show that 150 schools and colleges have taken up the offer. The mayor’s office said last night that more schools were expected to do so.

Geoff Barton, general secretary of the Association of School and College Leaders, said that the rise of knife crime had created “a sense of urgency and alarm” but that schools remained “oases of safety compared to the streets outside them”.

He said: “I would encourage schools and colleges to seriously consider this offer, not only to give reassurance to parents and teachers but also to act as a deterrent.

“If there were anyone thinking of taking a knife into a school, this would be a way of reinforcing how completely unacceptable that would be - even to contemplate it.”

On Wednesday night, IT student Israel Ogunsola, 18, was stabbed to death in a street in Hackney, east London. And on Easter Monday, 16-year-old Amaan Shakoor was shot in the face outside his former school, Kelmscott Secondary School, in Walthamstow. He later died in hospital. Another boy, aged 15, was stabbed in the same attack and suffered life-changing injuries, police have said.

Last year, Mr Khan said schools were reluctant to discuss knife crime owing to ‘stigma’ fears, and he called on Ofsted to treat the protection of pupils from knife crime as a safeguarding standard.

Ofsted said today that inspectors and researchers had started a “mixed methods study” to find out how schools are safeguarding pupils from the threat of knife crime.

The study, which will culminate in a report in the autumn, will include a questionnaire survey to schools and a series of school visits.

An Ofsted spokesperson said: “Schools, colleges and others who work with young people have a vital role to play in protecting children from knife crime and helping them make positive decisions about their lifestyle choices.

“And Ofsted is determined to support this important work. This is why we are undertaking a report to look at how schools in the capital are safeguarding pupils against the threat of knife crime on their premises and how pupils are being educated on the dangers of carrying a weapon.

“We want to help heads make informed decisions so that they can keep children safe. The report will focus on London but the messages will resonate in other cities and towns where youth violence exists.”

The knife detectors can be used at individual school events, or high-risk schools may choose to use them regularly to screen students entering the premises. Headteachers will have the final decision on how they are deployed.

Schools can request a knife wand through their safer schools officer or by emailing Knifescreeningwands@mopac.london.gov.uk