Fathers are to be given the same rights as mothers to take up to a year off work to look after newborn babies, ministers will announce on Friday.

Under the proposals, which will take effect in April 2015, parents will be entitled to share existing “maternity” leave of up to 50 weeks between them – and have the right to return to their old jobs at the end of the period.

Employees will be able to request the time off in blocks, or split it up across the year, but businesses will be able to insist that all leave is taken at once.

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The announcement is a significant victory for the Liberal Democrats, who fought off concerted efforts by Conservative Cabinet ministers to water down the proposals. These included the Tory Chairman Grant Shapps, the Defence Secretary Philip Hammond and the Health Secretary Jeremy Hunt, all three of whom are said to have argued that the measures put an unnecessary burden on business.

The shared parental leave of up to 50 weeks under the new plan does not include an additional two weeks reserved for the mother for recovery after birth. Employees will have to give their employer eight weeks’ notice of their intention to take shared parental leave, which they can do either before or after their child is born.

Employers who offer enhanced maternity leave above the statutory minimum will have to offer the same terms to fathers as mothers.

The changes may be of particular financial benefit to families where the mother is in a higher paid job than the father. However, the Government could not explain how its new rules would prevent couples from “gaming” the system by both claiming the enhanced maternity pay.

In addition, all parents of children under 18 will have the right to take up to 18 weeks of unpaid parental leave per parent per child per year. At the moment this right only exists for parents of children under the age of five.

Announcing the changes, which will require legislation, Nick Clegg, the Liberal Democrat leader, said women should not have to choose between “a successful career or having a baby .... We want to create a fairer society that gives parents the flexibility to choose how they share care for their child in the first year.”

Mr Clegg added: “Many businesses already recognise how productive and motivated employees are when they’re given the opportunity to work flexibly, helping them retain talent and boost their competitive edge. This is good for families, good for business and good for our economy.”