You may or may not recall this but Ken Livingstone, when Mayor of London (well, sort of, wasn't he?), brought in a policy that we here at the ASI had long championed, the Congestion Charge. And now we see another London Mayor thinking about bringing in a further policy which we have equally championed, pay per mile driving.

London is to consider pay-per-mile road pricing and banning car parking in new developments under plans to cut 3m car journeys a day in the capital.

A transport strategy to be published on Wednesday by the London mayor, Sadiq Khan, will set targets to ensure 80% of journeys are made by public transport, walking or cycling.

Khan said: “As London’s population is set to increase beyond 10 million, our future health and prosperity is more and more dependent on us reducing our reliance on cars.

“We have to be ambitious in changing how our city works. While there will be 5m additional journeys being made across our transport network by 2041, at the same time we’re setting ourselves a bold target of reducing car journeys by 3m every day.

Of course, much of this is barking inanity. Having a target for the number of journeys is simply nonsense. Set the basic rules and then leave people be to sort it out themselves by responding to the incentives.

But the basic idea of the charging per mile driven is entirely correct. We've a scarce resource, road space. We need to design some method of allocation of that scarce resource. And resource allocation is almost always best done by price. Thus, charge people for use of the scarce resource.

Space on the Embankment at 4 am is not scarce so there need to be charge. Space in the same place at 4 pm is scarce and thus a charge should be made. Technology has moved on since the original Congestion Charge so we are indeed able to bring in a more fine grained solution.

We're not, as we've noted, enamoured with the ideas of targets and so on. But the basic underlying concept is indeed correct. Charge people the correct price for a scarce resource and the correct amount of said resource will be used.