Conservative politicians spend much of their time criticising their Labour counterparts for the often-inefficient way in which they spend public money. This is often quite justifiable: the many billions wasted through disastrous PFI schemes, abandoned IT projects and expensive-but-pointless gimmicks under Labour are a shameful legacy.

But the gap between this Tory rhetoric and reality is often rather stark, and nowhere is this more evident than with the Mayor of London, Boris Johnson.

Take, for example, one of Boris’s pet projects of a cable car to transport people between the O2 arena and the Excel exhibition centre (both Olympic venues). Sounds like quite a nifty idea, doesn’t it?

And it sounded even more attractive when Boris and Transport for London said that it would cost just £25m and be paid for in its entirety through private finance.

Unfortunately, though, TfL got its figures wrong – the estimated cost was updated, to £45m. Quite a jump.

And now, thanks partly to some judicious questioning by Mike Tuffrey and Caroline Pidgeon, it’s emerged that they missed another few things off their calculations (including, apparently, ‘land acquisition’ – something I would have thought would be quite crucial). The new estimated cost of the Thames cable car is £60m.

Not to worry, I guess – at least Boris assured us the money would all be found privately.

But it seems the project has hit a bit of a buffer there, too: only £36m of private capital has been raised to fund the project.

And where is the remaining money coming from to cover the shortfall? You guessed it: TfL’s rail budget.

So those fair increases that we were promised would be spent on improving London’s creaking rail network will actually be spent on an unnecessary pet project of Boris Johnson’s.

All that leads me to conclude with this question: exactly what sort of conservative is Boris Johnson? Not a fiscally responsible one, that’s for sure.