Nothing I have so far said should be taken in any way as a denigration of science. The achievements of science have been, and no doubt will continue to be, greater than the achievements of economics. But what is at issue is the crucial distinction between the physical world and human behaviour. I realise that this is getting (in theory) dangerously close to the vexed question of free will — one of the few remaining philosophical problems not to have been either resolved by scientific understanding or dissolved by the exposure of linguistic muddle.

But in practice this is a non-issue. The plain man says: "I have to believe in free will: I have no choice"; and that is good enough for me. But I must say, en passant, that I am far from sure that the superiority of science (when it sticks to its extensive last) over economics is matched by a corresponding superiority of scientists over economists. 

Certainly, nowadays, when it comes to public policy, scientists have come to resemble a new priesthood, intoning the orthodoxy of the day and seeking to cast out heretics, whereas economists appear to be in perpetual disagreement with each other, a somewhat healthier state of affairs however much it may dismay the policy-maker seeking informed advice.

Or, in the words of that wise economist, John Kay: "People who trained as scientists do not very easily think in terms of numbers and probability distributions. They cling to stories, and that is the way they proceed and that is the way they lead their lives. As an economist, I used to suffer from a kind of physics envy, but I have come to realise that as an economist I was probably better trained to think about controversial issues than I would have been if I had been a physicist."It is indeed remarkable that science, whose achievements were made possible by the enlightenment and the age of reason it brought forth, is far too often nowadays seeking to become a new religion, while it falls to economists in their modest way to cling on to the torch of reason.

Myth No.2

So to myth number two: that policy-makers should be guided by the precautionary principle. This can be disposed of rather more briefly, since — while a beguiling alliteration — on examination the so-called precautionary principle crumbles into meaninglessness. Insofar as it has any meaning at all, it oscillates between the precept "be careful", to which the correct response is "of course", and the precept "you can't be too careful", to which the correct response is "oh yes you can".

If you can't be too careful you would never travel by air, train or car. You would probably never even cross a road. According to Professor Lofstedt and Dr Fairman of the King's Centre for Risk Management, there are no fewer than 19 different formulations of the so-called precautionary principle — and none of them has sufficient precision usefully to inform policy decisions. This is perhaps unsurprising given that there are usually at least three dimensions of uncertainty. There is the assessment of the risk you might choose not to take, or at least to reduce. There is the assessment of the risk that you might be devoting substantial resources which might be better used in some other way. And there is the extent to which you are (or perhaps should be) risk-averse — something which is likely to vary from person to person and, perhaps even more, between different societies and cultures at different stages of development.