[UPDATE: Boris Johnson withdrew his original claim in a Mayoral response  made on 19th September 2012. CTC welcomes his retraction].
Answering Mayoral Questions  on 23rd May 2012, he said (after 2:31.40):
"I've seen a figure, I think, of 62%, which is the high proportion of cycling KSIs that are associated with some infraction by the cyclists themselves of the rules of the road."
[N.B. "KSIs" means killed or seriously injured].
Well, I don't know what data Boris thinks he was quoting, but I'm very certain he's wrong. Wildly wrong.
For a start, the Government doesn't collect data showing who was found to be breaking what laws when cyclists get injured - nor for any other types of road user, for that matter.
For another thing, his 62% figure is a long way out from other data sources which he might have got muddled up with.
The most likely source of his confusion is some data published in a report  by the Transport Research Laboratory (TRL), showing who the police think contributed to collisions involving a cyclist and a motorised road user (driver or motorcyclist). The report contains graphs  without actual numbers or percentages, however CTC has obtained these subsequently from TRL.
What these figures show is that:
- In collisions between a cyclist and a motor vehicle where they police attribute “contributory factors” (CFs) to one or both road user, they allocate CFs to the cyclist only in 36% of cases, to the driver only in 53% and to both users in 11% of cases.
- However the police are a good deal more likely to blame the cyclist if they are either a child (which seems harsh), or if they have died (which seems harsher still, given that they aren’t there to tell their side of the story). Cyclists in their late teens or early adulthood are also disproportionately likely to be blamed (but less so than children),
- On the other hand, cyclists aged 25+ are thought to be solely at fault in just 24% of their KSI injuries (or 20% if you include collisions of all severities). The driver is held to be solely at fault in 67% of these collisions, with both being blamed in 9%.
- For cyclists aged 25+ who are killed, the proportions are 34% to the cyclist, 54% to the driver and 13% to both. However, for cyclists in this age-group with serious or slight injuries, the percentages are much lower. They are thought to be solely at fault for 23% of their serious injuries, with 67% being blamed solely on the driver, and 9% on both parties. For slight injuries to this age group, the proportions are 19% to the cyclist, 71% to the driver and 10% to both.
The full set of percentages is as follows:
Of course, contributing to a collision does not mean you have necessarily breached the rules of the road. Indeed these figures are only the impressions of the police officer making the initial report of the collision - they are not the results of any detailed investigation, let alone court action.
There is one other source  which Boris might have got confused with is some London-specific data for 2007, 2008 and 2010 (they didn't analyse 2009 for some reason). It shows who was making what manoeuvres when cyclists were seriously or fatally injured.
Of all the cyclist KSI injuries for these 3 years, 5.3% involved red-light jumping or disobedience of a junction control by the cyclist, 15.1% by a driver or motorcyclist. A further 4.9% involved a cyclist riding off a pavement. Other data shows, unsurprisingly, that this is an offence much more likely to be committed by children - so it isn't actually an offence at all if they are aged under 10.
However, this source suggests that the two predominant cyclist offences only account for around 10% of serious or fatal injuries in London.
So it is very hard to see where Boris gets his 62% figure from. I think we should be told.
CTC believes that all road users should respect the rules of the road  and the safety of other road users. However, spouting nonsense 'statistics' merely stokes up antipathy towards cyclists from the irresponsible minority of drivers, and that has to be damaging to road safety. Politicians need to behave responsibly too.