Jeremy Corbyn's economic policy deserves more attention than it's getting.

It seems to me that this comprises two necessarily related elements. One is higher corporate taxes: he wants to "strip out some of the huge tax reliefs and subsidies on offer to the corporate sector" - which he claims to be £93bn a year. This would depress investment, by depriving firms of some of the means and motive to invest. However, this would be offset by "people's quantitative easing" - a money-financed fiscal expansion:

The Bank of England must be given a new mandate to upgrade our economy to invest in new large scale housing, energy, transport and digital projects.

This amounts to what Keynes called a "socialisation of investment":

It seems unlikely that the influence of banking policy on the rate of interest will be sufficient by itself to determine an optimum rate of investment. I conceive, therefore, that a somewhat comprehensive socialisation of investment will prove the only means of securing an approximation to full employment; though this need not exclude all manner of compromises and of devices by which public authority will co-operate with private initiative. (General Theory, ch 24)

This is a response to a genuine problem - low capital spending. The share of business investment in GDP has (in nominal terms) been trending downwards since the mid-70s.

Quite why this has happened is unclear: I suspect it owes more to fundamental problems of a lack of monetizable investment opportunities than to short-termism, but this doesn't much matter for current purposes. Corbyn's view seems to be that, if private enterprise won't invest, the public sector should.

I don't have much problem with the diagnosis here. But I do with the remedy, for three reasons.

First, how exactly will the public sector investment projects be chosen? One reason why the Bank of England didn't conduct QE through the corporate bond or equity markets was that it didn't think it had the expertise to pick companies. So how can it appraise energy and digital projects?

One answer to this is to have a National Investment Bank. But again, where will its expertise be drawn from? I fear this is a form of managerialism - a faith in central managers.

The second question is: who will do the actual investing? There's a case for the state to invest in infrastructure. But we also need corporate investment, to raise private sector productivity.

It's possible that the higher aggregate demand created by people's QE will stimulate private sector investment via accelerator mechanisms. Maybe high expected demand will overcome higher corporate taxes. Or maybe not.

My third problem is raised by David Boyle: where are the mutuals? Corbyn's world seems to comprise just two actors: the state and capitalist corporations. There seems insufficient emphasis upon decentralized forms of economic control, be they Robin Hahnel's participatory planning, Roemerian market socialism or workers' control.

Granted, Corbynomics might be a building block towards these. But as it stands, it looks to me like replacing one set of bosses with another - which isn't as egalitarian as it could be.

Nevertheless, Corbyn is at least asking the right question - how to stimulate investment - which is, sadly, more than his rivals are doing.