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“The family vote is a critical battleground, and Labour needs to push back on the assault from the Conservatives on these voters,” said Mark Penn, the American polling guru who now advises Labour.

“From 1997, it has consistently been the case that women have backed Labour, so the way for the Conservatives to get in is to to extend their traditional appeal to men by trying to make themselves about the family, thereby getting the women’s votes.”

Richard Reeves, director of the left-leaning think tank Demos, said that the party that best understands the needs of modern families will have a competitive edge. “Politically there are high stakes here,” he said. “The broader questions of gender, family, the roles of fathers, the pressures of balancing work and family life are the stuff of everyday life for millions of voters.”

This valuable electoral group is also constantly talking to itself, both at the school gates and in online forums. In recent months mothers of young children have found their political voice through the website Mumsnet.

It began life as a place for parents to share tips on pushchairs or vent frustrations over their babies’ erratic sleep patterns, but its popularity has meant that politicians now queue to join the site’s online discussions. Brown recently felt the wrath of the Mumsnet inquisition when he refused to name his favourite biscuit.

However, the site also campaigns on more weighty political issues, and has become a leading voice in the campaign to keep childcare vouchers.

Carrie Longton, co-founder of Mumsnet, said: “Our parents are people they need to win over: they’re opinion formers and early adopters. I’m sure parents have always been important, but they’ve just not been as visible before.”

Cameron was quick to identify this emerging social trend perhaps because he and many of his inner circle are parents of young children. George Osborne, the shadow chancellor, and Michael Gove, the influential schools spokesman, both have youngsters of nursery and primary school age.

“The top Tories are quite involved in their families’ lives,” said Reeves. “It is known that you can’t get Tory frontbenchers to events on Saturdays, because they protect family time quite aggressively.”

The party will go into the election with a series of pledges. These include fully flexible parental leave: the idea would be that each family would be allocated nine months of paid leave. It would be up to the parents to decide who would take it and when.

“We are moving away from the concept of maternity leave, and involving both parents in the early years of their children,” said Maria Miller, the shadow families minister. “If fathers are involved in the early years of their children’s lives, it can have a dramatic impact on reducing family breakdown.”

The Conservatives are keen to give all parents with children under 18 the right to ask for flexible working, which surveys show is top of the wish list of parents struggling to juggle work and family lives.

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