On his day, of course, Livingstone rattles away merrily. He stands there, head on one side, in his strange-looking suit, like Ken Dodd but with better teeth. He loves to hold forth on subjects that are outside, or marginal to, his remit. This is the man, after all, who has pronounced with gravitas on matters as extraneous as the state of the stand-off between the Russian parliament and presidency - albeit on the losing side. But when it comes to subjects that matter to Londoners, like today's politically motivated stoppage - evasiveness.