WOMEN face a widening pay gap with their male counterparts once they start a family, a study by a leading economic think tank has found.

The Institute for Fiscal Studies (IFS) found that while the overall "gender wage gap" had narrowed over the past two decades, women with children were falling behind.

The study, carried out for the Joseph Rowntree Foundation, found that on average, hourly pay rates for women are currently around 18% lower than for men. That compares with a gap of 23% in 2003 and 28% in 1993.

However once women started a family, gap widened consistently year by year so that by the time their first child had reached the age of 12, their hourly pay was 33% down on men.

The report suggested the difference may be down to women working fewer hours once they have children and, as a consequence, missing out on promotions - or simply accumulating less labour market experience - while their male colleagues pull further and further ahead.

It also found the closing of the overall wage gap was down to improvements in the pay rates of less well-qualified women, who did not have A-levels or other higher qualifications, while for better-educated women the gap had remained unchanged for 20 years.