LONDON (Reuters) - More mothers in England are working than 20 years ago and more fathers of toddlers are choosing part-time work, partly because of fairer policies like shared parental leave, free childcare and flexible work hours, according to official data on Tuesday.

The number of working mothers rose to 4.9 million in 2017 from 3.7 million in 1996, the UK's Office for National Statistics (ONS) said in a report.

Meanwhile, fathers balancing part-time jobs and young children almost doubled to 7 per cent in 2017 from 4 per cent in 1997, which ONS has attributed to policies like flexible work hours and shared parental leave.

"The doubling of free childcare from 15 hours a week to 30 hours in England is just one of a larger number of initiatives designed to improve education, make childcare more affordable, and to encourage parents back into work," the report said.

"The introduction of flexible working practices and shared parental leave have also made it easier for fathers to share childcare responsibilities," ONS added.

Yet most working mothers in England are in part-time jobs, a trend that has remained stable since 1997, it said.

Among parents of young children, almost all fathers have jobs, while mothers with are least likely to be employed, ONS said.

Job shares and working from home are key to boosting women's salaries, the country's equality watchdog Equality and Human Rights Commission (EHRC) said in August, as British women earn 18 percent less than men for the same job.

Closing Britain's gender pay gap could add 150 billion pounds (S$271 billion) to the country's annual gross domestic product by 2025, according to consulting firm McKinsey Global Institute.