For Gordon Brown, it was a question too far. When the Prime Minister went on the parents’ networking site Mumsnet yesterday to do his first live webchat, he had answers ready on every topic he could imagine, from childcare vouchers to climate change.

But there was one question that he steadfastly refused to answer: what’s your favourite biscuit, Prime Minister? The question was put to Mr Brown no fewer than 12 times (which, as it happens, is the exact number of times Jeremy Paxman put his question to Michael Howard in the notorious 1997 Newsnight interview).

Time and again they asked what has become a staple question of Mumsnet interviews. “May I ask you what your favourite biscuits are?” said one mother. “What biscuit, Mr Brown, please, before you leave!” pressed another. Steadfast to the end, Mr Brown refused to answer. One member, MadameDefarge, said: “Maybe he needs to consult with his advisers on what would be the most vote-winning biscuit to admit to liking?”

Afterwards 10 Downing Street still refused to comment, although it is known that he used to snack on up to three Kit Kats a day before his wife got him to cut down.

Justine Roberts, managing director of Mumsnet, said that biscuits had been provided for Mr Brown’s visit to their office in North London, and that Mr Brown been “munching away on the shortbread very happily”.

While Mr Brown’s visit to the site fell short of the disaster of Tony Blair’s speech to the Women’s Institute when he was slow handclapped, it was still a sharp reminder of one of the great unwritten rules of politics: never mess with mums with attitude.

He spent just over 70 minutes fielding questions on subjects ranging from bankers to Afghanistan, as well as more predictable topics such as child tax credits, midwives and the Cambridge report on primary education.

The first indication that the encounter might not be an unqualified success came when he was asked if he thought he had been an unlucky Prime Minister. “Not when I’m sitting here at Mumsnet!” he replied, in a less than subtle attempt to charm his audience. They remained uncharmed.

“That has to be the cringiest thing I have ever read,” wrote sagan.

“Is anyone else disappointed with the quality of the answers so far?” wrote sitdownpleasegeorge. “Please engage with a little depth Gordon.”

When hatwoman asked about the ending of childcare vouchers, Mr Brown told her they were not being abolished, it was just that the Treasury was phasing out the tax and national insurance relief. “Oh Mr Brown — not abolishing them but phasing out the tax relief?” she wrote. “Could you tell me pray how, then, a child care voucher will differ from, erm, cash?”

Mr Brown signed off with an address on why everyone should vote Labour, which began by talking about Britain facing the biggest choice for a generation and ended with an direct attack on the Tory party.

“Ask them — how can you deliver change when you so clearly haven’t even changed your own party?” he said.

Once more the mothers were unimpressed. “I think a lot of people are cross at the political broadcast at the end,” said cleanandclothed. “Badly misread the audience there.”

“He’s lost my vote for good,” wrote FlamingoBingo. “I’m absolutely livid!”

Ms Roberts said there were 850 posts on the thread by the time he left, with about 500 questions. “He was never going to get through all of them. This was his first live web chat and it takes a while to get into the language and to get the tone.”

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