WOMEN managers are effectively working for free for 57 days a year because of a gender pay gap, according to a new study.

A survey of 72,000 managers found that women in equivalent full-time jobs earned 22 per cent less than men.

The difference means they are working for an hour and 40 minutes without pay every working day, said the report by the Chartered Management Institute (CMI) and wage analysts XpertHR.

The gender pay gap for professional roles averages £8,500 a year, rising to almost £15,000 for senior staff, it was discovered.

The gap gets wider as women grow older, ranging from six per cent for women aged 26-35, to 38 per cent for the over 60s, said the report.

The research also showed there were fewer older women in executive positions.

Women outnumber men in junior management jobs, but fewer than one in four are on company boards, just short of a 25 per cent target set by a Lord Davies-led study.

Ann Francke, chief executive of the CMI, said: "Working for free two hours a day is unacceptable. While some progress is being made, it's clear from our research that Lord Davies is right to target the executive pipeline.

"Having more women in senior executive roles will pave the way for others and ensure they're paid the same as their male colleagues at every stage of their careers."

It comes after a separate study by CMI last year revealed that the gender pay gap among managers in Scotland had widened to an average of £8,347 a year.

The study showed that the average salary of male managers this year was £36,119 but for women it was just £27,772 - a 30 per cent pay difference.

However, reforms ushered through parliament earlier this year are set to force all large businesses across Britain, including almost 500 in Scotland, to publish the difference in average pay for their male and female workers before the end of March next year.

Companies with fewer than 250 employees will be exempt but campaigners hope that the increased transparency will force larger firms to do more to tackle gulfs in remuneration, more than 40 years after the Equal Pay Act came into force.

The CMI report, published today [Tuesday], said said pay transparency was a "powerful driver" for closing the gender gap.

Mark Crail of XpertHR, added: "An entire generation has now worked its way through from school leaver to retirement since the first equal pay legislation came into effect in 1970, yet the gender pay gap persists, and many employers still prefer not to know just how bad it is in their organisation rather than getting to grips with the data and doing something about it.

"HR and reward specialists in larger companies have a special responsibility to get this firmly on to the senior management agenda and to develop the plans needed to close the gap."

Minister for Women, Equalities and Family Justice Caroline Dinenage, said: "We have more women in work than ever before, 25 per cent of boards are now made of women and the gender pay gap is the lowest on record - and whilst I am proud of the progress made, we must go much further.

"This is why we will be requiring companies with 250 or more employees to publish their gender pay gap, to ensure the economy fully benefits from women's talents and fairly rewards them.

"I would encourage all companies to have their say on the consultation to help us eliminate the gender pay gap in a generation."