Get a grip on London's gang violence, Boris challenges Ken

The Tory mayoral candidate attacked the lack of leadership from City Hall as he called for a concerted policy - bringing together the Mayor, police and charities - to tackle the problem.

Mr Johnson also demanded that police be issued with scanners that enable them to detect weapons without having to search suspects.

His call for action comes after Faridon Alizada, 18, was stabbed to death in Erith, south-east London, early on Saturday. Last week Henry Bolombi, 17, was killed after getting off a night bus in Edmonton - adding to the 27 deaths recorded last year.

Mr Johnson today announced a detailed set of policies to reverse the surge in knife crime and castigated Mr Livingstone for treating the killings as "strange news from another planet".

He wants mobile scanners used in "hot spots" such as Tube stations and on large crowds travelling to festivals, noting the haul of weapons that resulted from a British Transport Police operation at a carnival in 2006.

Writing in today's Evening Standard, Mr Johnson said: "Just after Christmas, a kid was stabbed to death round the corner from me in Islington, in broad daylight, in front of hundreds of horrified shoppers. Two days ago there was another terrible stabbing, this time in Bexley.

"We cannot allow 2008 to be as bad as 2007, when 27 London teenagers were murdered. It is time we got a grip on the culture of the gangs and gang-related killings - and the first step is for City Hall to stop treating the problem as though it were strange news from another planet.

"It is a scandal that so far we have heard little or nothing on it from the Mayor, the Commissioner of the Metropolitan Police, or the Home Secretary. We need positive action, a short, medium and long-term strategy for getting us out of this mess."

He calls for the use of both portable arches and powerful hand-held devices, suggested by former Met commissioner Lord Stevens, to enable officers to search a suspect from a distance without having to go through the legal - and often ethnically controversial - processes of making an official stop.

Other ideas include:

Making it his "number one priority" to stamp out knife and gun crime if elected Mayor.

Ending "political correctness" in the way he says police question suspects.

Guaranteeing London Development Agency funding for community sports projects.

Funding community groups such as the Eastside Young Leaders Academy, which uses tough mentoring schemes to divert teenagers from crime.

Trialling live CCTV coverage on 20 of the most crime-ridden bus routes.

He also called for a more visible policing and less paperwork which keeps trained officers off the beat, a concerted effort to boost public confidence in the police to make sure they felt it was worth reporting crime and all new buildings in London to be designed to make crime more difficult, meaning an end to walkways and dimly-lit stairwells. Mr Johnson pointed to the BTP's Operation Shield, which he said recovered 90 weapons including 57 knives, a taser, knuckledusters, four CS and pepper spray canisters and batons in one day during the 2006 Luton festival. Mr Livingstone has backed the use of knife scanners in schools but is less keen on installing permanent scanners at Tube and train stations.

During his visit to India last year he saw one in Delhi, installed by authorities fearing a terrorist attack on the underground. At the time the Mayor said it would be impractical to search every Tube passenger at peak times. Liberal Democrat mayoral candidate and former Met deputy assistant commissioner Brian Paddick has spoken frequently of the need to address the number of teenage knife killings.

He wants to pass the form-filling burden of police officers to community support officers to enable them to get back on patrol as quickly as possible

after an arrest. Mr Paddick said the spate of killings was "not a temporary aberration but a fundamental shift in culture among our young people". He added: "We need more than the usual combination of downplaying the issue and ineffective, cosmetic initiatives. I am determined to use my 30 years of policing experience to come up with solutions."