the party 's deputy leader harriet harman , in an interview with the daily mail , said grandparents would be allowed to take up to four unpaid weeks off per year in order to help with childcare .
she said the policy , to be unveiled in labour 's women 's manifesto , would require a change in the law and would help millions of working families .
more than half of mothers rely on grandparents for childcare when they first go back to work after maternity leave .