Wrong, wrong, wrong. The Prime Minister, Mr Cameron, apparently excuses the ministers who were involved in the botched award of the rail franchise for the West Coast mainline on the grounds that they could not have been expected to spot the mistakes amid pages of numbers.

Unpick the Prime Minister’s surprising ignorance of how large projects are judged. The allotment of a rail franchise is very similar exercise to approving a major investment in new facilities. You have to decide whether projections of costs and usage running many years forward make sense. You don’t run your eye through sheets of number trying to spot wrong ones. What you do is go to the assumptions and challenge them in detail. You ask to review the supporting evidence. You look to see whether in light of your own experience the approach and the results are plausible.

This is what, say, a museum director would have to do if asked to approve plans for an extension, or a charity boss if asked to invest in a new service, or a business executive if asked to approve building a new plant.

But all this is too difficult for government ministers. The former Secretary of State for Transport, Justine Greening, should have had some idea, having worked as an accountant before entering politics. But the poor Minister of State at the time, Theresa Villiers, had no relevant experience of any kind. Before she became an MP, she was a barrister and a lecturer. The problem with career politicians is that they don’t know how to govern.