As the man who first exposed the financial inexactitude behind Boris Johnson’s “new Routemaster” proposals I’ve got to say I’m amazed that six week later he’s still getting his abacus in a twist about the cost of the scheme.

Actually, other people are in a muddle about it too, but Boris’s latest comments are making matters even worse for him. The story so far:

Episode One: Boris tells Vanessa Feltz it would cost £8 million to put conductors on the existing bendy bus routes. The following day, Ken Livingstone claims it would cost £80 million, though his website swiftly reduces that to £70 million. They can’t both be right.

Episode Two: I ask TfL to tell me what it thinks the conductors would cost, and to make an assessment of the cost of implementing the entire Johnson “new Routemaster” policy, buses and all. They think it would cost £49 million for the conductors and a total of £112 million a year to put the whole thing into effect. This means TfL thought both candidates were wrong on the cost of conductors, Boris by the most. Team Ken, however, immediately claimed victory with regard to the overall figure because it nearly matched their estimate of £110 million. In fact, they reached that figure by a different route from TfL: they had a higher figure for conductors but forgot to include the cost of hiring the additional drivers that would be required if existing passenger capacity was to be maintained (double deckers can carry fewer passengers than bendys, so you’d need more of them, hence more drivers). I did point this out to them at the time, but they weren’t about to look a gift bus in the mouth and, after all, I suppose they could have stuck on a bit extra for the drivers if they’d been so inclined.

Episode Three: Team Boris accuses TfL of being “highly mischevious” and said it stuck by its £8 million figure. The suggestion that TfL was deliberately generating Ken-friendly figures was repeated in an Evening Standard article on 19th March, despite TfL’s estimate having been broadly confirmed by the independent company TAS in the meantime. But, of course, the TfL figures were at odds with Livingstone’s as well as with Johnson’s. Funnily enough, the Standard story didn’t mention that.

Episode Four: On Newsnight, Boris Johnson still wouldn’t offer a total figure for his “new Routemaster” policy. His earlier defence - the one his campaign presented to me - had been that you can’t reliably estimate the cost of a bus that has yet to be designed. This might not be very satisfactory, but at least it sounds plausible. Instead of it using it, though, Johnson claimed it would cost about the same as Livingstone’s proposed “hybrid” buses. And he again failed to make clear that the £8 million figure referred only to the cost of conductors. True, it was miles out, but not £100 million out, and could have been finessed - as his campaign team did in response to my questions - as enough for an initial roll out, one which Londoners could be said to support.

Episode Five: In a well-executed sting operation, Johnson revealed to an undercover Livingstone supporter that he did, in fact, have a figure for his new Routemaster scheme - “about £100 million,” which is pretty close to the £110 million the Livingstone campaign had said right at the beginning, and the £112 million TfL said it would be - the very calculation Team Boris told me it was “highly mischievious” of it to have provided. Result? A somewhat vague but, nonetheless, serviceable and potentially popular policy looking a complete and utter mess.