Men should work less and their employers and the government should help them to do so in order to close the gender pay gap, according to a thinktank.

A report from the IPPR says there is a gender pay gap in 80% of clearly defined occupations. “This points to seniority as a critical driver of the pay gap: for most occupations, men are in more senior, high-pay versions of the role than women,” said Catherine Colebrook, IPPR’s chief economist and co-author of the report, The State of Pay.

All companies with more than 250 employees were required to publish their gender pay gap for the first time in April, and the data showed that eight out of 10 companies paid women less on an average hourly basis than men.

The IPPR report says the majority of companies reported a gap that was smaller than their industry average, suggesting that even if the UK’s larger companies closed their gender pay gaps, a disparity would persist at a national level.

“What this report tells us is that firms are a big part of the solution to fixing the gender pay gap but they can’t do it on their own,” said Colebrook. “The solutions also have to come from individuals and from government. In short, men need to work fewer hours and women need to work more.”

Colebrook pointed to the “motherhood penalty”, by which the gender pay gap increases sharply after women take time out of work to have children and find their ability to progress in the workplace after returning is curtailed. According to research from the Institute for Fiscal Studies undertaken for the Joseph Rowntree Foundation, by the time a first child has reached 20, mothers earn almost a third less per hour, on average, than similarly educated fathers.

The IPPR report argues that new ways of making sure women keep pace with their male counterparts on pay and seniority are needed. “Women are less likely to negotiate salaries when starting a new job and when in post, so employers could rule out the possibility of negotiation altogether or make sure all employees earn at least as much as any new recruit on the same level,” said Colebrook.

She said women were less likely to pursue promotions, and suggested employers could automatically consider employees for promotion after a given length of time in post, interview all internal candidates for vacancies, and encourage more women to apply for internal promotions.

Companies could also advertise that salaries were negotiable, offer successful candidates the option of a colleague to negotiate on their behalf, and match salary offers to make sure all employees on the same level earn as much as a new recruit.

More roles needed to be flexible, and more senior roles should to be offered as a job share, she added.

But changing the behaviour of fathers – for example, encouraging them to take shared parental leave and work part-time – was also needed, she said. The report states: “Employers should encourage more men to work flexibly and to take time out for caring responsibilities.”

Colebrook said: “Changing men’s working behaviour is a crucial component of equalising pay. Employers could offer paid paternity leave on a ‘use it or lose it’ basis, make jobs flexible by default and encourage men to job-share.”

Mary-Ann Stephenson, director of the Women’s Budget Group, said the report painted a depressing picture but highlighted what could be done differently. “Closing the pay gap is not just about employers. We all need to tackle the unequal distribution of care work, the gendered division of labour within the workforce and, ultimately, the type of work that we value and reward within society,” she said.