Here:

Does an education at an elite public school diminish a politician’s legitimacy? Gordon Brown’s dismissal of David Cameron as “just an Old Etonian” signifies not just his view that products of privilege have no place in politics, but also that the electorate will, as a matter of course, reject him ab initio because of his background.

Boris Johnson’s election as mayor of London appears to have put paid to that idea. There could hardly be a more caricature Old Etonian than the foppish Johnson, but it did not stop voters in the most cosmopolitan city in the world from electing him. Far from seeing him as a pre-modern relic, they relished his postmodern idiosyncrasy.

I think “didn’t stop” is right, and all this may even have helped.  After all, the real story of these elections was that the voters wanted to give Gordon Brown, and his government, and his party, a good kicking.  If that meant putting on Boris Johnson as a boot, so be it.  It was one of those “we’d vote for a pig rather than these bastards” elections.  The worse - the less legitimate, the more risible, the more of a posh pig - many voters still reckon people like Boris Johnson to be, the more forcefully that point was made.