Why is the Mayor still silent on these killings?

No, it's not happening in some faraway land. It's happening right near where you live. Just after Christmas a kid was stabbed to death around the corner from me in Islington, in broad daylight, in front of hundreds of horrified shoppers.

There have already been two teenage murders in London since the New Year dawned: on New Year's Day a boy was murdered in Edmonton, and two days ago there was another terrible stabbing in Erith, in south-east London.

We simply cannot go on at this rate. 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.

This matters to London. The capital needs leadership on this problem, and 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.

It is just too easy for us to shrug and say that it is all to do with massive social changes - family breakdown, loss of parental control, rampant materialism. Those may be factors but they do not mean we can do nothing. We can't just keep turning the pages of our papers in search of brighter news.

It is time for a concerted policy to tackle the scourge of teenage gang killings, and that co-ordination is surely the paramount job of the Mayor. If people feel the streets of London aren't safe, that negates so much of the other good work being done by the police. If people feel that a neighbourhood is unsafe, they don't invest there: they don't open shops or restaurants or buy houses - and we entrench the huge social and economic inequalities in this city.

To make those streets safer, we must of course begin with the police. It's not just a question of ensuring a more visible police presence, and cutting the paperwork that keeps so many officers in the back room.

We need a clear signal - from the top of the Met - that tackling the gangs is a priority. We need to do far more to end the prevalence of knives and guns on the streets and on public transport, and it is time we at least considered the use of remote hand-held scanners that can detect weapons at a distance.

The idea has been promoted by Lord Stevens, the former Commissioner, and it has the advantage of allowing officers to "search" without stopping, and without being seen to victimise some communities. We need to prevent the teenage gangs from treating the buses as getaway cars, and intimidating other passengers.

That's why I have proposed a trial of live CCTV on some routes, so that the police can see the violence taking place as soon as they are alerted to it by the bus driver - and immediately go to the scene. We should have tougher sentences for knife crime, and we should be ending the growing culture of public cynicism that means we now have an epidemic of unreported crime.

That culture is wrong and defeatist and it emboldens the criminals. We should be making sure that all new building in London is designed to make crime more difficult; and that means no more vulnerable walkways or dimly-lit stairwells - no more repetition of past mistakes.

But we will never deal with this problem unless we also understand the positive reasons why kids seek out gangs. In some ways, their choice is rational. The gang provides a sense of security, and an opportunity to earn the esteem of their peers. The gang can be a kind of family; and that's why we should be doing so much more to allow them to obtain these benefits - excitement, competition, achievement - in other ways.

The Mayor could be doing so much more to encourage competitive sport of all kinds, with all its potential for developing emotional maturity and allowing young males to let off steam. There is so much that could be done with the arts.

But above all, we should be using mayoral funds to encourage the thousands of volunteers who are working with the kids - and their parents - to nip the problem in the bud, trying to steer them away from criminality, because that is the best way to save the taxpayer millions.

At the weekend I was out in Southgate with the Street Pastors, an extraordinary and inspiring movement that has grown hugely in the past four years. I talked to a few of the kids loitering around at 11.30pm, but two stick in my mind. One was a 15-year-old who bragged (convincingly) about the hundreds of offences he had committed, the drugs he had taken and the relative failure of the police to deal with him.

I could see all too easily how he would end up in prison, at massive expense to the state. Then there was another kid, in the same gang, who said he was doing an NVQ to qualify as an electrician. He said he could not wait to earn so much that he would be able to show off to a certain policeman who had persecuted him.

For him, I saw more than a glimmer of hope, and I saw how the Street Pastors were helping him. There are people across London who are doing work like the Street Pastors - XLP, Prospex, Kids Company, East Side Young Leaders Academy - and what we need to do now is to bring all these people together into a Londonwide network. We should involve the City, too, where its money can make a real difference. Where necessary, we should be helping such groups expand with London Development Agency money, and not wasting it, like the current administration, on pointless, politically correct agitprop.

But above all, we need to take London's gang culture seriously if this year's toll is not to be a tragic repeat of 2007 - or worse. This is a huge task for London and I am determined to do something about it. For now, the question remains - why have we heard nothing but silence from City Hall on these killings?