It's widely, though not universally, agreed that the Labour party has not advanced the interests of the worst off by as much as it might have. The right complains that the welfare state has created a "dependency culture" whilst the left complains that it has been insufficiently redistributive. This poses the question: why has the party not done more to help its natural constituency?

Standard accounts focus upon "betrayal" or - for the right - the unintended consequences of (mild) redistribution. However, a new paper has another explanation. Andrea Vindigni and colleagues use a game-theoretic model to show that it is in the interest of leftist party leaders to act against the interests of the poor:

Policies that reduce the income of the poor relative to the average income...paradoxically consolidate the political power of the Left. This is because these policies make the natural constituency of a left-wing party endogenously more dependent on it and, therefore, increase the support for the party itself.

They give the example of left parties supporting bad educational policies or free trade and migration, but we could add anti-union laws and less redistributive policies than the left would like.

And there's good evidence that, when the working class does get richer, support for the left wanes. Some of Thatcher's support came from part of the (southern) working class that had done well thanks to the long post-war boom.

Vindigni et al's analysis suggests that there are two things which make anti-poor policies especially likely. One is if left parties' leaders obtain high private benefits from being (or having been) in power. The other is if they fear an ideological shift to the right, say because they are intellectually insecure or because they fear the (perhaps mythical) power of the right-wing press. Both were features of the New Labour government.

How should we interpret this paper? It might be just another example of economists seeing something happening in practice and wondering whether it's possible in theory.

But there is another reading. The paper shows, or reminds us, that there are structural pressures upon leftist governments to disappoint their constituents - or, in other words, that we should be sceptical about the efficacy of a parliamentary road to socialism. In this sense, we have yet another example of how mainstream neoclassical economics vindicates a Marxian insight.