Mr. Cameron calls his wife, Samantha, his “secret weapon,” and she is turning out to be just that, with an increasingly prominent role in the campaign. It helps that she is relatively young (38) and photogenic, with a name that lends itself to delighted tabloid punning. “Wham Bam! Sam Cam to be a Mam (She’ll Need a New Pram),” The Sun reported last month, when the couple revealed they were expecting a baby in the fall.

Prime Minister Gordon Brown’s wife, Sarah, 46, is an active participant in his career, functioning as the designated humanizer of a man who can seem dour, distracted and dysfunctional. Mrs. Brown, a constant Twitterer with more than 1.1 million followers, is also active in Mumsnet. The site began as a virtual meeting place for mothers but now, with 850,000 members, is seen as a potent political force, both a reflection of and a way to influence a group that functions as the British equivalent of the American soccer mom.

“Mumsnet is totemic of the modern mothers who will be the key political battleground at the election,” Deborah Mattinson, a pollster for Mr. Brown, told The Times of London recently.

When Mumsnet celebrated its 10th anniversary at a lavish party at the Google offices here last month, the prime minister himself turned up to pay tribute, telling the guests that the site was part of a “social revolution” that was “changing the way Britain lives.” (In her own speech, Mrs. Brown said that Mumsnet was “like having a new doting mum, a new no-nonsense mother-in-law and a new supernanny all rolled into one.”)

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And so much has the site seeped into the public debate that when Mr. Brown, 59, seemed to duck Mumsnetters’ queries about his favorite cookie in his online interview — having already discussed issues like taxes and nuclear weapons — his opponents used it as a chance to torture him politically.

It wasn’t his fault; the prime minister hadn’t seen the question (and the answer is “everything with a bit of chocolate in it,” he said later). But the confusion did not stop The Daily Mail from reporting that Mr. Brown was “apparently unable to decide what the politically correct answer ought to be.” And it did not stop Mr. Cameron from taunting him in Parliament.

“Are we really going to spend another six months with a prime minister who cannot give a straight answer, cannot pass his own legislation, who sits in his bunker not even able to decide what sort of biscuits he wants to eat?” Mr. Cameron sneered.

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But Mr. Cameron went on to suffer a new Mumsnet-related embarrassment in his own online chat, when he floundered on the question of the National Health Service’s allotment of free diapers for disabled children.

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The online mothers were not pleased when he said he would have to look into it — especially because as the father of a disabled son, Ivan, who died last year, Mr. Cameron might have been expected to know a thing or two about the issue. Realizing he had committed a faux pas, Mr. Cameron meekly traveled to Bristol for tea with, and a talking-to from, the mother who first asked the diaper question.

The mother, Riven Vincent, said Mr. Cameron had admitted that: “Sam said to me, ‘For goodness’ sake, Ivan got four a day.’ ”

Other politicians, including Nick Clegg, the Liberal Democratic leader, and a number of cabinet members have also been interrogated on Mumsnet, and the Labour and Conservative Parties have sought advice from the site’s founders.

But “What do women want?” is a notoriously treacherous question, and some women are indignant both at the notion that their entire gender speaks with one voice and at the candidates’ touchy-feely methods of courting their support.

“Politicians once needed to prove their trustworthiness, efficiency, authority,” the columnist Cristina Odone wrote in The Daily Telegraph. “Apparently these days they need an emotional hinterland to appeal to voters.”

Ms. Odone added: “I’m sick of the feminization of politics. If it means having to meet Dave’s mum, Gordon’s auntie and Nick’s granny, give me macho politics any time.”