I would hazard a guess that David Cameron is ambivalent about Boris Johnson’s bid to be London’s mayor. Winning the capital would be a big boost for the Tory leader. On the other hand, once in City Hall the quixotic Mr Johnson might blow it. The ensuing chaos would call into question the Conservatives’ fitness for office nationally.

So when you ask Mr Cameron about the contest, the answer comes in two parts. The first says that this is an important chance to shine. If the Tories are to force Gordon Brown from office they need to grab a sizeable clutch of seats in the capital. Momentum matters. Winning in London’s multi-ethnic melting pot would say that Conservatives are back in touch with modern Britain.