Dominic Cummings tells all that Boris Johnson signed off on HS2’s £100 billion costs on the basis of inaccurate - fanciful to laughable in fact - projections of future passenger traffic. This being obviously true, it’s just that all of this was known a decade back, as we’ve repeatedly pointed out.

Boris Johnson signed off on the £100 billion High Speed 2 rail line based on "garbage" data predicting an exponential increase in demand for the service, Dominic Cummings has claimed.

In a posting on the Substack website, the Prime Minister's former chief adviser, said that he and other officials had highlighted "absurdities" in the evidence presented to Mr Johnson to justify pressing ahead with the construction of the line last year.

But Mr Johnson "blew" the decision on whether to go ahead with the scheme having been presented with a "garbage model/graph", Mr Cummings wrote.

This is not something new. As we have indeed been pointing out for a decade now.

For HS2 has never actually passed a properly done cost benefit analysis. The underlying assumption is that business, or working, time spent in a train carriage is unused, worthless, time. So, if those business, working, people get to their destination faster they have more working time available and this is, really, the major benefit on offer from HS2. It’s by far the largest amount of money on that benefit side.

Except that 21st century technologies, the laptop, mobile phone and internet - OK, possibly 20th century technologies - make that assumption about the 19th century technology of the railways untrue. People do work while travelling these days therefore the reduction in travel time isn’t worth what is being assumed.

This is such an obvious point that it even made George Monbiot choke on his cornflakes when he was told it. And if you’re making an economic error that even Monbiot can see through then you are, obviously, making a real doozy.

The question then becomes well, why in heck is it being built? The answer being concentrated benefits and diffuse costs. That £100 billion becomes, for us out here, £1,500 each in costs. Or, perhaps more accurately for how we care about it, £75 a year per man woman and child in the nation for a couple of decades.

Yes, this is real money, it’s a cost for us to bear, but it’s not an amount we’re about to storm the barricades over. On the other hand those who are to receive the £100 billion are a small group who are really very, very indeed, interested in their receiving this bounty from the rest of us. Therefore we have a concentrated political interest fighting a diffuse not very interested at all. Guess who wins in politics?

Which brings us to our actually lesson from all of this about HS2. Politics - therefore government - is a lousy way of not just getting infrastructure built it’s a terrible way of deciding which and what infrastructure to build. HS2 being our perfect exemplar - it wasn’t worth it back when it was only going to cost £17 billion but it now continues at £100 billion.

The solution is equally obvious. Insist that those who wish to build infrastructure do so with their own money, not our.