It is a fact insufficiently acknowledged that making good public policy is difficult. Really difficult. The government has an annual budget in excess of £700 billion and responsibility for the health, wealth, safety and education of a nation of 70 million souls. It rarely knows exactly what effect any policy decision will have. It nearly always will be making choices that make some of us better off and some of us worse off.

Yet political debate is almost always conducted in terms of absolutes: this is right, that is wrong, austerity is needed to save the nation, austerity is destroying the country, Brexit is an entirely good thing or wholly bad. It may be Boris Johnson who is famous for telling us we can have