As it is, they now know he is committed across the river at City Hall until his term finishes in 2016, or at least they think he is. If Boris can find a way of getting a seat at the next election, and combining it with the tail end of his mayoralty, he will surely do so.

For the chancellor, whose leadership ambitions have been dealt what should be seen as a fatal blow by the disastrous reaction to his recent Budget, the eventual return of Boris will be problematic. Osborne cannot be leader. At a gathering of normal non-politically-obsessed people, try mentioning the thought that he might one day hold the top job and watch the reaction.

That means the chancellor's best hope after Cameron is to try and become a king-maker and then retain his exalted position in the hierarchy. He may have to choose between backing Boris or gambling on a rival such as Education Secretary Michael Gove being strong enough to win by that point. Other Conservatives, from the excellent last two parliamentary intakes, may by then also fancy a run at the leadership, pitting Boris's star power against their earnest and commendable hard work on policy and ideas. None of this wrangling is as far off as it might sound. If Cameron loses the next election the Tories will be choosing a leader three years from now, and even if he wins he is determined to avoid going on much beyond the middle of the next parliament.

His critics frequently say that Boris has no discernible following in the parliamentary Tory party, but many MPs care most of all about holding on to their seats. If there is a sense that enough of Britain buys Boris, then when the moment comes there will be MPs who sign up. 

The danger for the country, and the Tories, is that all of this is seen through the prism of celebrity and personal ambition, when there are such vast economic, constitutional and cultural challenges confronting the nation.