Tuesday evening offered the entertainment of seeing a well watered (but not, I insist, inebriated) think tank wonk dancing in the street shouting "Eureka!", "Eppur si muove", "it works!" and similar. The reason for this display of entirely unedifying proof that white middle aged men indeed cannot dance was that there was a window cleaner cleaining the windows of the pub.

Yes, yes, I know, Worstall's finally lost his rocker and fallen off the plot. But note the most important word above: evening.

The window cleaner turned up to do the pub's windows at 10.30 at night. And your corresponding think tank wonk asked why: "Congestion charge innit. Used to cost me a fortune so now I do my round at night". And thus is one of the Adam Smith Institute's long running campaigns vindicated.

For decades now the ASI has been saying that the way to deal with congestion is to price it. This changes incentives, changed incentives change behaviour and thus charging will reduce congestion. It was Ken Livingston who actually brought the Congestion Charge in, not quite the exact method we would have chosen, but it is at least a start, a proof of the basic concept of road pricing.

For as our window cleaner has explained, that very charge has moved his cleaning rounds from commuting type times, when the roads are crowded, to non-commuting times, when they are not. Which is the point and purpose of the whole thing.

At which point, "Eureka!", "Eppur si muove" and similar.

BTW, if you happen to have windows in central London in need of a regular cleaning drop me an email and I'll pass on Ted Johnson's number to you. Least I can do for one providing the empirical proof of a nice theory.