News that Boris Johnson has been rebuked by the UK's independent statistics watchdog for making unwarranted claims about the success rate of a resettlement unit he set up at Feltham Young Offenders Institution may not surprise those familiar with the mayor's past form on data dissemination. As recently as March Sir Michael Scholar, the UK Statistics Authority 's chair, told Boris that his "selective prior release" of figures about crime on London's public transport was "poor practice" and "damaging to public trust." Journalists attending a photo opportunity in Finsbury Park had been handed spreadsheets telling a good news story based on stats that had yet to be placed, unvarnished by any politician's commentary, in the public domain. If that strikes you as a petty technical gripe, reflect instead on Boris's using the occasion to associate himself with falls in bus-related , Underground and DLR offences that happened four months before he actually became mayor and ten months before he oversaw increases in the numbers of police officers dedicated to reducing bus and transport hub crime. To this suspicious behaviour we might add the fact that - as one of Boris's own publications shows (see graph on page 33 ) - these types of crime fell at a faster rate under the previous mayor Ken Livingstone and conclude that there's good reason to treat with caution any intimation by Mayor Johnson that he deserves credit for crime reductions in this category, welcome though they are. At this point we could digress to consider London crime statistics Boris doesn't talk about, such as the large rise in the number of teenagers and young adults injured with knives that occurred during the first three years of his mayoralty, the small, steady increases in acts of serious violence against under-20s since 2008 or the hikes in robberies and all forms of knife crime that have happened in the past twelve months. But let's instead return to those inaccurate claims about the performance of the resettlement unit at Feltham. Described as a major element of the mayor's Time for Action strategy for youth, it was set up in Heron wing in September 2009 and has beds for 30 inmates who are serving their first custodial sentence and been judged receptive to changing their ways. Last month, in the wake of the London riots, Boris told the House of Commons home affairs select committee that re-offending rates among those leaving Heron been cut from 80% to just 19%. He'd already made a similar claim in a press release last November and an article for the Sun in June. In his Telegraph column a couple of weeks after speaking to the committee he asserted that "re-offending rates have been brought down from about 80 per cent to about 20 per cent." The truth is that the re-offending rate so far is much higher, and Boris himself has now been obliged to admit to BBC London that it is in fact 40%. It seems that rate could be as high as 50% when a fuller assessment has been made. Sir Michael Scholar has written to home affairs committee chair Keith Vaz, saying that, "the Mayor's evidence to your committee is not supported by the Ministry of Justice's published statistics; nor is it supported by any statistical analysis published by the Mayor's office." A background note attached to the letter says that the Mayor's claims "do not appear to stand up to scrutiny." The note adds: We understand that the figures for re-offending at the Heron Unit come from internal, unpublished, management information. We also understand that the management information contains the following caveat: "This is based on anecdotal information and does not represent a re-conviction rate and should not be used publicly." And yet it was used publicly, and by none other than Boris Johnson himself. I like the mayor's stress on the need for more effective rehabilitation of young offenders, and in time he may have solid grounds for hailing the Heron unit initiative a success - albeit not as great a one as he's been saying to far. But when it comes to peddling dodgy numbers about crime, he's becoming a serial offender. Boris Johnson London London politics Crime UK criminal justice Youth justice Dave Hill guardian.co.uk © 2011 Guardian News and Media Limited or its affiliated companies. All rights reserved. | Use of this content is subject to our Terms & Conditions | More Feeds