A report by the Equality and Human Rights Commission said the proposal would increase the take-up of leave among fathers and lower-income parents, help tackle the gender pay gap and give better support and social benefits for parents and children.
Rather than extending maternity leave, the report said that fathers needed to have more paid leave in their own right and parents needed the option of choosing how to share leave.
Under the proposals, the first 26 weeks would remain dedicated maternity leave but the number of weeks that mothers are paid at 90 per cent of pay would rise from six weeks to 26 weeks. This would be followed by at least four months' paid 'parental leave', that either parent can take, any time up until the child's fifth birthday.
Fathers would keep the current entitlement of two weeks' paternity leave but it would be paid at 90 per cent of pay.
The scheme, estimated to cost £5.3 billion, would be phased in gradually by 2020.
A YouGov survey of 4,500 parents carried out for the Equality and Human Rights Commission found that 54 per cent of fathers with children under one said they felt they spent too little time with them.
Duncan Fisher, co-founder of the Fatherhood Institute, said the report was the 'best-ever contribution to the debate about how parents share work and care'.
The Family and Parenting Institute said the plan offered real choice for parents and an opportunity to share caring responsibilities.
Further information
The report, 'Working Better', is at www.equalityhumanrights.com