Labour has the most leftwing leader in its history. So how, in this election, did the party present a policy programme that would increase child poverty? It is a troubling question that casts a long shadow over the party’s hugely successful campaign: a campaign that in other regards stood out for its conviction and moral clarity.

The disconcerting truth is that Labour’s manifesto policies would have raised living standards for the top half and cut them for the bottom. Firstly, the party failed to promise to end huge benefit cuts that will drive a million people into poverty. The share of national income spent on benefits would have plummeted, abandoning Gordon Brown’s belief in sharing the proceeds of growth through redistribution.

Furthermore, although Labour – according to the Institute for Fiscal Studies – pledged income tax rises for the top 2%, the party’s plans for public services would have left higher-income households better off on average. The manifesto offered “something for nothing” to the top half – with new universal entitlements to childcare, school meals, university, lifelong learning and social care – but did not ask the vast majority to pay any more in tax or social insurance to fund them.

Social democrats in the Fabian tradition have long supported universalism in the welfare state, and the inspiring promise of a lifelong national education service is something that everyone on the left can get behind. But in setting out its plans Labour ditched the cherished Beveridgean ideal, that universal entitlements should be used by all and paid for by all. The new frontiers of the welfare state, including an end to tuition fees, were to be funded by “other people”: not just the super-rich, but the victims of the welfare cuts too.

So how was it that Labour stood on a programme that would have widened the gap between rich and poor? Or, to put it another way, why did the manifesto end up being more statist, but less redistributive than when Labour was last in office?

Electoral politics might be part of the answer. Promising to raise benefits or asking people to pay for new public services is not a huge vote-winner. Then again, the Liberal Democrats said they would do both. And Labour’s manifesto did not just say things to be popular: that’s why it was a refreshing change. These electoral considerations can’t have been the only reason.

‘The manifesto offered “something for nothing” to the top half – new universal entitlements to childcare, school meals, university, lifelong learning and social care – but did not ask the vast majority to pay any more in tax or social insurance to fund them.’ Photograph: Alamy

Could the answer lie closer to home, in the Labour party’s internal workings? It seems that, at the heart of the party, no one made the case for higher social security. Labour’s vocal membership was not campaigning for it and the unions prioritised their members’ jobs and pay. Their lengthy wishlists dominated the manifesto but they did not fight for better benefits, and so failed low-income Britain.

Next time, the expertise and talent of the whole of the party must be drawn upon. Much of it is on the backbenches, and MPs should be asked by the leadership to sit on commissions to develop new ideas. It is time for Labour to rediscover a professional, empirical approach to policy. For example, not enough people knew that a high minimum wage is no substitute for tax credits in tackling child poverty.

Labour needs fewer easy slogans and more nerdy homework.

And policies need to be considered in the round, not as discreet propositions. It was only by looking at the whole package of tax and spending plans that their inegalitarian impact became clear. Similarly, each individual idea for extending state activism sounded reasonable enough. But the nationalisation proposals as a package felt like distant, 1970s statism, rather than a democratisation of the economy to put more control into people’s own hands.

Labour exists to spread power, wealth and opportunity, not to expand the state for its own sake – a lesson learned long ago by Fabians. And in that context, the fight against poverty should have been at the front of the policy queue. Labour used to know that egalitarianism trumps state socialism; that collectivism must be based on contribution; and that evidence and practicality beat hopeful dreams. Next time Labour writes a manifesto, it needs to think harder.