More than 40 years since legislation was introduced which outlawed paying men and women different wages for the same work, women still face a lifetime of earning less. New figures from the Office of National Statistics show the pay gap is beginning to widen, after years of slow but steady progress. Looking at mean average earnings for people working full time, women's pay has gone up by 1.3% an hour – from £14.07 in April 2012 to £14.25 in April 2013. Over the same period, men's hourly pay increased from £16.52 to £16.91 – a 2.3% increase.

This means the gender pay difference for full-time employees (excluding overtime) has widened to 15.7% – an almost 1% rise on last year's 14.8% gap. Considering all employees, so including both full and part-time workers, the situation is even bleaker – the average gap in pay has jumped from 18.6% in 2012 to 19.1% in 2013.

A range of things contribute to the gap. Occupational segregation, where men and women cluster in different sectors is a major factor. Jobs traditionally done by women, such as cleaning and catering, are undervalued and paid less than jobs traditionally done by men, such as transportation and skilled trades. Research out this week from the TUC found that 98% of apprentices in construction and vehicle repair were male, while more than 90% of childcare and hairdressing apprentices were female.

This is one of the reasons why women make up the majority of those earning the minimum wage or less. Outdated, rigid working practices also have an impact. Women still tend to do the bulk of unpaid caring – looking after children and elderly relatives – so the lack of flexible working practices can mean they lose out on promotions and training opportunities. The dearth of "family friendly" jobs also means many women who would like full-time work have to settle for part-time jobs – women make up the vast majority of part-time workers – which typically pay far less per hour than full-time jobs. In a survey of 2,500 mothers by community website Working Mums earlier this year, 70% said more flexible working would aid them in their career development. Plain old sexist discrimination also plays a role, with women being paid less for the same work simply because of their gender.

News that the gap has begun to widen is a damning indictment of the government's record when it comes to women's standing in the economy, and could not come at a worse time. Women's incomes are being squeezed on all sides – two-thirds of the savings from benefit caps and cuts are coming from women's pockets, while what little money is being put back into the system is disproportionately benefitting men, who will make up 85% of those whose incomes rise as a result of the £700m pound marriage tax allowance.

Drastic cuts to the public sector workforce risk undermining progress on women's pay as the Fawcett Society has long warned. Women working full time in this field face an average 13.6% gap, as opposed to 19.9% in the private sector. With more than a million jobs expected to be cut from the public pay roll in the next few years, 2013 could well mark a watershed moment in the fight for equal pay, when years of progress began to go into reverse.

The government should take action on a range of fronts. First, protecting and Increasing the value of the national minimum wage. Two-thirds of minimum wage workers are women; low pay is – in essence - a gender issue. Increasing it, at least in line with inflation, would help tackle the pay gap.

Second, introduce mandatory pay audits. Relying on voluntary action isn't working. The government must implement section 78 of the Equality Act 2010 which would require big businesses – those employing more than 250 people - to measure and publish data on their gender pay gaps. Greater efforts to tackle occupational segregation would also help ensure longer term change to our skewed labour market.

Tackling the gap is not rocket science. We know what causes it and we know how to fix it. What's missing is the political will. Failure to take action – and urgently – means another generation of women will be consigned to a lifetime of low, unequal pay.