Women who take a career break to have children lose out in the salary stakes when they return to work compared to female colleagues who have stayed on the career ladder.
Women who remained in their careers saw their wages rise over a seven-year period by an average of 15 per cent. But for those who took time out during the seven years to look after children, the rise in wages was less - equating to 2 per cent a year less for each year out of employment.
Together with higher salaries in typically 'male' professions, the wages gap between the sexes in Britain is the largest in the European Union, according to a study by Sylvia Walby, Professor of Sociology at Leeds University, and Wendy Olsen, lecturer at Manchester University. And the pay disparity between men and women is on the rise.
According to the study, men earn 25 per cent more, with average pay at £10.27 an hour for men and £7.50 for women.
Women in typically 'male' occupations are paid 53p an hour more than those in traditionally 'female' jobs, such as cleaning and secretarial work.
Earlier this year, an analysis by Incomes Data Services (IDS) found that the huge pay rises awarded to a small number of male executives meant that the gender pay gap in the UK actually widened in 2002, a reverse of a 20-year trend
IDS also found that within particular occupations, the pay gap is at its widest among company financial managers and treasurers (where women's average hourly earnings amount to some 60 per cent of men's) and at its narrowest among check-out operators and retail cashiers (where women's average hourly earnings amount to more than 99 per cent of men's).
Miss Olsen said employers fail to take into account the skills women gain from bringing up children. "The importance of motherhood in women's pay is nil," she said. "It is their labour market experience that counts."
The authors say the pay gap relating to mothers can be bridged only by providing more training for returning women. "The Government puts a lot of effort into getting the unemployed back to work but not enough for women whose careers have been interrupted," said Miss Walby.