An interesting comment here from the Office for Budget Responsibility:

In an interview with The Telegraph, Mr Miles conceded that the OBR's central forecasts published on Wednesday were “almost guaranteed to be wrong”, adding that the watchdog had faced accusations of being both “ridiculously optimistic” and a “bunch of pessimists”.

The problem here is not with the people - the Treasury. NIESR, the IFS, varied bank models and so on are all as bad - but really is in our stars. It is not possible to model something as complex as the economy to the sort of level of detail people are trying to.

This is of course Hayek but Hayek applied to macroeconomics rather than the details of microeconomic policy like trying to determine what the price of bananas should be.

It’s the implication of this fact that is so important. Given that the model is impossible then attempts at management by the model will not work either. The best that can be done is some vague and broadbrush idea - try not to collapse things, nor set off an inflationary spiral - and the rest of it has to be left to take care of itself.

That detailed demand management so beloved of Keynesians simply does not work. Not just for political reasons - those sunny days when deficits should be reduced never do seem to arrive - nor worries about the theoretical linkages of the models. But because we simply cannot produce a model reliable enough to allow us to make forecasts and thus tinker.

We’re actually rather left with the idea that macroeconomics as a management tool isn’t very useful. Which is fine by us of course. We’ve long said that if we get the nuts and bolts of incentives and price setting mechanisms - markets - right then the macroeconomy will be emergent from that. She’ll be right when she arrives cast in all her raiment too.

That is, it’s not so much don’t meddle as you’ve not got a clue what you’re doing so don’t meddle. Which, come to think of it it, is useful advice for so much of life, not just political control of the economy.