Labour will examine whether people should be allowed to take unpaid leave to look after grandchildren, Harriet Harman will say in what the party hopes will prove a popular move with female voters.

The Deputy Leader - who has been touring the country in a controversially-coloured pink bus in a bid to drum up support - is presenting a mini-manifesto aimed specifically at women voters.

Alongside extending free childcare to 25 hours, an additional 50,000 childcare places, age-appropriate compulsory sex and relationship education and stronger laws and a new commissioner to enforce national standards on tackling domestic and sexual abuse, it will commit to a consultation on helping grandparents be more involved in childcare.

Ms Harman said existing employment practices had not kept pace with social change, pointing to research suggesting 1.9 million grandparents give up a job, reduce their hours or take time off work to look after their grandchildren.

One option that would be considered by a consultation should Labour win power on May 7 would be to allow them to share in the 18 weeks of unpaid parental leave - no more than four in any one year - available to parents over the first 18 years their child's life.

'There have been many ways in which family life has changed, but public policy remains rooted in the past,' she said ahead of the launch.

'This was evident in conversations I had across the country as part of the work of the Older Women's Commission.

'Labour has a better plan for working families. The sharing of parental leave with grandparents could give families more flexibility by recognising the important role that grandparents play.'

Shadow business secretary Chuka Umunna said: 'Many companies recognise the benefits of flexible working to retain valued employees with caring responsibilities, and some are already recognising the pressures on grandparents.

'But the system is outdated. We need to look at how to make parental leave more flexible so that it works better for families and businesses.'