For this, according to the Chancellor yesterday, “is becoming the school-gate election campaign”. A million-strong group of mothers will wield a powerful influence on the result.

A survey by netmums, an online network for mothers, found that Labour’s support had more than halved among its members since the last election. This is by no means a scientific survey — the respondents were not picked at random and they are not representative of all mothers of school-age children. But the results may still make Labour politicians blanch.

Of the 3,000 women who chose to respond to the survey, 40 per cent voted Labour at the last election, but only 17 per cent say that they are certain to do so again on May 5.

By contrast, Conservative support is up one point to 15 per cent, and the Lib Dems are down two to 15 per cent. Labour’s former supporters seem to have migrated to the “don’t knows”, who now make up 42 per cent.

What is more, 43 per cent of the mothers said they would change their vote if another party could persuade them that it was tackling their key issue. So what are the things that these women really care about?

According to the netmums survey, the most important are support for stay-at-home parents, education, feeling safe, flexible working and food quality. Oddly, health did not enter the top ten.

Siobhan Freegard, a spokeswoman for netmums, thinks that this may be because children are now rather better served by the NHS: they are seen relatively quickly both by GPs and casualty departments. Politicians of all parties have been struggling to meet the demands of these mothers, who are an influential and politically promiscuous segment of the electorate.

The Conservatives have now cottoned on: Michael Howard has come out with a childcare policy, which he announced a couple of weeks ago.

Labour spotted the potential quite a lot earlier and to some extent the other parties have been playing catch-up.

In the early 1990s, Labour thought of childcare and flexible working as slightly marginal “women’s issues” and the Tories treated them as an apolitical, private matter.

By the time Labour won power, though, these questions had moved up the political agenda, thanks mainly to pressure from increasingly powerful women in the party, such as Harriet Harman, Tessa Jowell and Patricia Hewitt. In his early spending rounds Mr Brown agreed to allocate money to nursery education, SureStart and childcare.

The Conservatives at that stage were still bemoaning the greater burdens on business that more flexible working or generous maternity leave would entail.

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