It must have seemed like such a good idea to someone to run Boris Johnson as the Conservative candidate for Mayor of London. It seemed he had very little chance of winning, but would raise the party’s profile and, frankly, fill the embarrassingly huge gap that no-one else was coming forward to be the Tory candidate. But then, just as in 2000, the voters of London made the calculation that in the grand scheme of things the Mayoralty of London wasn’t really that important, and so seized the opportunity to vote for the maverick outsider candidate as a cost-free way of showing their displeasure to the occupant of Downing Street.

And so we get to see what a new-style “post-nasty party” Cameron Conservative government would actually do, through what Boris and the Conservative team are doing in City Hall. And make no mistake, Boris may be a one-man maverick, but for exactly that reason, those close to Cameron have foisted on him their top team of managers, to make sure that it is not just a goofy Boris show, but a proper Conservative government of London.

All of which makes it all the more significant that it’s not working out well.

This week Boris’ “First Deputy Mayor” left the team, the third senior figure, and second Deputy Mayor, to leave that team in some disarray (there have also been one or two more routine departures).

Applying the Lady Bracknell test, this is really start to get pretty embarrassing. You cannot continue to lose one senior figure a month, and remain credible for very long.

I don’t think we should get hysterical about it: each of the three’s reasons for going have been fairly reasonable in themselves, changes do happen - and most importantly, having myself lived through enough attempts to stir up a Town Hall scandal where there isn’t one, I would say that no-one should make the mistake of thinking that any real Londoners actually care which person they’ve never heard of no longer occupies a post they didn’t know existed.

But what it does reveal is that the Boris Johnson mayoralty really does not know where it’s going.

If David Cameron walks through the door of Number Ten in a year or two’s time, people will expect him, as well as having some idea what he plans to try and do in there, to have some ability actually to do it.

Before you buy a bottle of “new and improved” perfume or aftershave, you spray a small amount out as a test, to see if it’s any good.

On this basis, why would you buy Cameron?