Many children in poor countries do not go to school. Gordon Brown thinks this a shame. On Thursday, in these pages, he announced his intention to provide every child on Earth with an education by 2015.

This will require a massive increase in the supply of education — millions more teachers and hundreds of thousands more schools. Yet it is perfectly doable, according to Mr Brown, because education is cheap in poor countries. An African can be educated for just £50 a year. Extending education to every child on the planet would cost only 2p per day per Western citizen.

Mr Brown is foolish to suppose that costs would remain unchanged under his scheme. In Africa alone there must be at least 40 million uneducated children. Assuming 40 per class, Mr Brown will need to recruit a million new African teachers. Does he really believe he can do this without driving up teachers’ pay? Does he think construction costs will not budge when he places his order for a hundred thousand new schools?

Mr Brown seems to have forgotten that the resources that provide education are scarce. New teachers will not descend from Heaven. They must be recruited from other occupations. More teachers means fewer farmers, doctors, policemen. Mr Brown’s scheme will divert resources in poor countries towards education and away from the production of other goods and services. It is a good idea only if this reallocation of resources improves on the current allocation, only if Africans are better off with more education and less other stuff. So, are they?

Mr Brown cannot know. He does not know where his extra educational resources will come from, nor what their current use is worth. For all he knows, recruiting millions of teachers in just nine years could cause economic calamity, decimating other important industries. But, whatever Mr Brown thinks, one thing is clear: Africans prefer their current allocation of resources.

Mr Brown concedes as much when he insists that education must be provided free of charge. If required to pay the cost of providing it, many Africans would not send their children to school. And if Mr Brown gave them not an education but £50, they would spend it on something else. In other words, these Africans value education less than it costs to provide. Which means that diverting scarce resources to education misallocates them. They would be better devoted to whatever Africans prefer to spend £50 on.

This will not bother Mr Brown. A man who thinks he knows better than British citizens what is good for them will surely think the same of uneducated Africans. Yet, even for a man endowed with Mr Brown’s heroic moral certainty, it seems presumptuous to plan the economies of foreign countries.