CMS has overhauled its parental leave package for UK staff and lawyers, potentially allowing new parents to stay at home with their child for several years before returning to the firm, rather than the standard 12-months.

The overhaul, which follows a move to more than double the paid maternity leave on offer to 26 weeks on full pay, unifies the different systems previously in place across legacy firms Nabarro, Olswang and CMS, which merged on 1 May this year.

It means new parents will be able to apply to take off longer than 12 months to raise their children, without harming their career prospects, with the extended leave on offer for same-sex and adoptive primary carers as well as new mothers.

The newly merged firm has also scrapped a 'claw back' provision that meant that those opting not to return to work after 12 months' leave had to repay some of their maternity pay to the firm.

CMS UK chair and senior partner Penelope Warne told Legal Week: "Most businesses and most law firms require people returning to work to come back after 12 months, and if you don't, your job can't be guaranteed. We have changed that bit. Although you're not being paid there's flexibility about welcoming you back after 15 months, 18 months or two years."

Warne stressed that there is no time limit to the extended period of unpaid leave. "Even at the extremes, even if you take the more extended period, we value our alumni and we would try to accommodate people."

She said that women will not damage their career prospects by applying for a longer period of maternity leave, and added that the new system applies equally to all new parents.

"If women take maternity leave it should not impact their career progression. I know from my experience at the firm that we have promoted female partners when they have been pregnant or early returners.

"There's no maximum time limit. What we are saying is we want to support our women in the business and I think that's a very important thing. We are very supportive of paternity leave as well. Whether male, female, straight, gay, your own child or adopted – all equally benefit."

Those taking parental leave will receive 26 weeks on full pay, followed by 13 weeks of statutory maternity leave. Until May this year the firm previously paid 10 weeks in full with 16 weeks on half pay, followed by 13 weeks' statutory maternity pay.

Earlier this month, US firm Morrison & Foerster (MoFo) also changed its maternity and paternity leave packages for employees and lawyers - with the exception of partners – in its London office.

Previously, the firm offered 13 weeks' maternity leave at full pay and 13 weeks at half pay. It has doubled its full-pay offering to 26 weeks, with statutory pay for the remaining 13 weeks of leave.

Meanwhile, it has extended paternity leave from two weeks at full pay to six weeks. The firm does not have clawback provisions in London for maternity and paternity packages.

A press spokesperson said the US firm would be "flexible" and "open to a conversation" with an employee who wanted to return to work at MoFo after 12 months.

The firm is currently reviewing its parental leave policy, with a view to paying more than the statutory minimum.