The London mayor has re-tuned his claims about serious youth violence in the capital. The move combines a tactical retreat with a flattering self-comparison with the record in this area of He Who Must Not Be Named (HWMNBN), the man known to the rest of the world as "Ken Livingstone". This was in evidence at Wednesday's mayor's question time in a carefully-staged exchange with Conservative assembly member James Cleverly about "tackling gang crime". It's interesting, I think, that the terms "gang crime" and "serious youth violence" have becoming increasingly interchangeable, even though they're not always the same thing.

Boris made plain that this "continues to be a major concern" (tactical retreat) and that when he came to office in 2008 "there was a lack of a co-ordinated approach to this issue" (flattering self-comparison with HWMNBN). He conceded that certain strands of his Time for Action programme aimed at saving young people from lives of crime, had not been as successful as he'd hoped (tactical retreat) but stressed that these were "a lot better than doing nothing" (flattering self-comparison with HWMNBN).

The tactical retreat shows Boris responding to being rumbled on Time For Action. Last month's observation by his "mentoring ambassador" Ray Lewis - formerly his "deputy for youth" - that the mentoring scheme had been "a disappointment" perhaps forced his hand, but Boris said he accepted that the scheme hadn't gone "as far and as fast as it should have done." Indeed, when I checked with City Hall last week the consortium he chose last June to deliver it across seven boroughs still hadn't finalised a local delivery partner for Haringey.

Boris also accepted that the rehabilitation scheme at Feltham he supports for young offenders jailed for the first time is "not perfect," and seemed to acknowledge that he'd previously over-claimed for it and that the recidivism rates of those who've been through it has been increasing.

However, he said he hoped that the efforts of the police in the form of Operation Blunt 2 have been "partially responsible" for what he described as "deaths of young people from knives" being "roughly halved," and at another point a fall in "teenage murders" from "roughly 30 to roughly 15."

These fatality figures are, well, roughly correct. The Met was able - at very short notice, for which I'm grateful - to find me figures for teenage homicides - murders and manslaughters - for the calendar years 2007 to 2011. The totals were 26 (2007); 30 (2008); 15 (2009); 18 (2010); and 15 (2011). These deaths were not caused only by stabbings, however. That was the most common cause in each year, though in 2007 nine were from shootings and in 2010, seven were. A small number of the homicides over the four year period were from physical assault, arson and head injuries.

Looking back to the original Time For Action document, published in November 2008, we find (on page 56) calendar year Met figures for teenage homicides going back to 2000. These show a pretty flat graph up to and including 2006, with the death toll always between 15 and 19. That pattern re-established itself in 2009-2011, which raises again the question of why a surge occurred in 2007 and 2008. Was there a particular reason at all? It also obliges us to ask why the fall back to previous levels has since occurred. Is it partially or at all a result of Operation Blunt 2? Would it have happened anyway? Can anyone be sure about any of these things?

As ever, we need to handle the statistics with caution. I stress that the ones I'm reporting here are for teenagers only. They therefore exclude under-13s, who are included in the Met's figures for "youth violence" overall, which politicians often refer to. They also exclude young adult homicide victims - people in their early twenties who, I'd suggest, are part of the age group we're really talking about when discussing "serious youth violence". Indeed, most of those arrested on the launch day of the Met's new anti-gang initiative were aged between 18 and 24.

Furthermore, the homicide figures tell only the most distressing part of the larger story. Kit Malthouse, who heads the new Mayor's Office for Policing and Crime, acknowledged at the first meeting of the equally new London Assembly policing and crime committee that the serious youth violence stats have been creeping up (an outrider for the tactical retreat?). But even these figures probably understate the problem. The Time For Action document says (page 59) under-reporting of incidents is likely to be high, meaning that "the actual extent of youth violence in London cannot be accurately established." I believe it.

What we do know is that the parts of London where territorial, postcode or "gang-related" violence are a major problem are generally acknowledged to have increased in number. Another change has been in the language used in this context. In the Time For Action document, gangs were barely mentioned at all. The only substantial section on them came in an appendix (page 61), where the numbers of people involved in "serious violent offending" are described as "small in comparison with the overall offending population" and their activities "concentrated in a limited number of areas and venues." These would enjoy far greater prominence today.

As for Boris's re-positioning, he's probably got it about right in terms of his battle with HWMNBN. There are plenty of people out there in London's youth work world ready to criticise Boris's performance. "The term 'chocolate fireguard' comes to mind," one such person told me the other day. But there are plenty who didn't rate Ken's efforts either. An opportunity exists for a brave and imaginative politician. Any takers?