Nick Clegg's announcement today that the government will go ahead with the implementation in April of Labour's plans to allow parents to share between them six months of maternity leave (three months of it paid) is an important one. This is not so much because of the reform itself, which is largely symbolic and will have limited practical effect, but because of what it says about the future of family policy.

Allowing parents to share leave between them is fine in principle, but for most families it will make little economic sense for the father to take time off work. The gender pay gap means that, for the vast majority of households, it is rational for mothers to stay at home. That is why the government itself estimates that only 4-8 per cent of eligible fathers (10,000 to 20,000 individuals) will take up the new right. And though the leave remains transferrable – for mothers to transfer to fathers – it reinforces assumptions of women as primary carers and men as breadwinners.

That is not to deny that increased choice and flexibility for families are important. But a liberal approach alone will not tackle the structural inequalities that shape those choices – in particular, the fundamental inequality in the division of work and care responsibilities between men and women. To tackle these inequalities, we need a more ambitious and extensive reform agenda that simultaneously advances childcare, employment rights and equal pay at work.

At the same time, elsewhere in government policy, spending cuts are pulling policy backward. Cuts in the childcare element of the tax credit reduce work incentives, while the design of the Universal Credit penalises dual-earner families. Meanwhile, Sure Start centres are being closed or refocused on poorer families, and despite the welcome expansion of nursery places for two-year-olds, support for children in their first year of life is being reduced as the baby element of the tax credit and Sure Start Maternity Grants are abolished.

For all that, however, Clegg is right to focus on narrowing the gap between the rights of women and men in our parental leave entitlements. The gap between what mothers and fathers can take in the UK – currently two weeks' paternity leave paid at the statutory rate for men, versus 12 months for women (nine months of that paid at the statutory rate) – is among the widest in the OECD. Unless fathers have more rights to paid leave, more fundamental inequalities will persist. The modern route to gender equality is to extend fathers' entitlements.

Under current fiscal constraints, bigger reforms – affordable universal childcare, better paid parental leave, and the "use it or lose it" fathers' leave that Clegg points to – are off the agenda for the foreseeable future. But it is important that policymakers do not simply account for these as public expenditure or business costs. With better childcare and parental leave rights, more women are enabled to work and use their skills productively after having children, rather than take up poorly paid part-time work. This increases the employment rate and improves the tax take. Full employment in the future will rest in large part on these foundations, which will therefore be fundamental to the affordability of the welfare state.

There is a broader political lesson here, too. Across Europe, the decade before the financial crash brought big increases in the female employment rate, particularly in the Catholic member states such as Spain. Countries with historically low levels of childcare provision, such as Germany, took a "Nordic" turn, significantly boosting their state support for families. In part, this was motivated by natalist concerns about declining birth rates. But it also reflected pressure from female voters who were no longer prepared to trade off their career aspirations against their desire to have children.

This dynamic is at work in different ways in all advanced economies. It provides an underlying momentum to reforms that strengthen family-friendly employment rights, childcare provision and gender equality in the workplace. The process of securing these goals is most advanced in the Scandinavian countries, which started down this path in the 1970s. Elsewhere, the "revolution is incomplete", as the sociologist Gosta Esping-Andersen puts it. But everywhere the pressure is the same: families want more rights to flexible work and childcare support, with more equity between men and women.

That is why the conventional conservative model of male breadwinners and female care-givers, buttressed by marriage tax breaks, is a political dead end. It has no underlying support from the deeper social and economic trends that are remaking our society. On this issue, at least, the future is progressive.

Nick Pearce is the director of the Institute for Public Policy Research (IPPR).