There are many jobs that require unpleasant personality traits, and you may think that politician is one of them. When I worked in the City, one of the requirements for promotion to partnership was “revenue hunger”. Greed is not something we normally admire, but we make an exception where our business partners are concerned. We also favour pedantic lawyers, frivolous game show hosts and merciless executioners.

So, what is Gordon Brown up to? In speech after speech he proclaims his profound goodness. We hear of his saintly parents and the moral compass they bestowed on him. It is “fairness” this, “decency” that and “social justice” the other. He casts himself as the kind of morally superior bore that any dinner party guest would be glad to find seated at the far end of the table.

I do not mean to suggest that Mr Brown is only pretending to be a goody-goody. But even if his sanctimonious self-characterisation is honest, it is still intentional. He must believe that moral superiority is a qualification for the job of prime minister. Or, at least, he must believe that we do. Thanks to focus groups and improved polling techniques, politicians understand the public’s preferences better than ever. And most choose to present themselves as people of deep moral conviction. From Barack Obama to David Cameron, those who seek office jostle each other for the moral high ground.

Loath as we may be to admit it, we vote for sanctimoniousness. Why? What makes voters think that moral superiority is a job qualification for politicians? The answer is that most have adopted the managerialist conception of the politician's job. They think that because politicians are asked to identify and then bring about good outcomes, that they should be people of extraordinary moral insight. Identifying the ends to which the nation’s resources and the state’s powers of compulsion should be turned is an awesome moral responsibility.

But this is where the public get it a bit wrong. Even if a politician is a good person, he can never really know whether he is doing the right thing. Because, as the economist Friedrich Hayek showed, such knowledge is humanly impossible. For example, Mr Brown has declared his desire to increase government spending on education to about £8,500 per state school pupil, this being the average spent on independent school pupils. It sounds like a jolly good idea. But how can he know this? It all depends on what we would spend the money on if not forced to spend it on education, and whether education is better than those alternatives. Yet no individual, no matter how special his morality, can know either.

Consider only your acquaintances. If you confiscated £1,000 of their income to spend on something you thought was “good” for them, how would they cut their spending on other things? Would they save less for their retirement, eat less nutritious food, give up their gym membership or what? You do not know. Nor do you know the value of what they will forgo compared with what you force on them. For that depends on their circumstances and their preferences – concerning which, again, you lack the required information. And if you cannot know what is good for your acquaintances, Mr Brown certainly cannot know what is good for the millions of British citizens he has never met.

Hearing of someone’s commitment to justice, decency and the British way is as uninformative as it is nauseating. Yet reading Hayek, though advisable, is not required to see through our pious politicians. Behind the posturing, our politicians lack the ability to answer even the most basic ethical questions.

Here is a simple one, posed by the economist Steven Landsburg. “Jack and Jill draw equal amounts of water from the community well. Jack’s income is $10,000 and he is taxed 10 per cent, or $1,000, to support the well. Jill’s income is $100,000, of which she is taxed 5 per cent, or $5,000, to support the well. In which direction is that tax policy unfair?”

Mr Brown and our other saintly politicians may love justice, but they say nothing of sufficient substance to suggest that they can answer this question. Yet, if they do not know what morality requires in such a simple imaginary case, how can they possibly know what it requires in the real world, with its unfathomable complexity?

Jamie Whyte is author of Bad Thoughts: A Guide to Clear Thinking

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