An interesting upshot from this post at my other blog. I think I’ve made a strong case that the structural features of the mayor of London’s job mean that there will always be tension between City Hall and Whitehall. It’s relatively hard to do anything truly new as mayor - so you’ve got to pick fights with the government in order to position yourself politically.

Therefore, the mayor will tend to be either the unofficial opposition leader, or aligned with whoever in the governing party is disagreeing with its policy. So how does that play out in a coalition context? When Boris Johnson made his comments about “Kosovo-style” cleansing, he was immediately attacked by Nick Clegg and Vince Cable before Downing Street got in on the act.

To some extent this is just of a piece with the way Nick Clegg’s become the coalition’s Baghdad Bob figure. But there are reasons for that - not only does Clegg have to signal that he’s committed to the coalition, he has to do so in ways that are costly and painful in order to carry conviction. And it’s useful for the government to have a coalition partner who can be used to discipline the Tory backbenches. Nobody wants an election, after all - the threat of it keeps the Lib Dems in line, the threat of losing the Lib Dems keeps the Tories in line.

So, a key forecasting principle: we’ll know there is serious tension in the coalition when Nick Cleggg agrees with Boris Johnson.