Sarah Palin dismissed criticism over the $150,000 (£94,000) spent on her clothes since becoming John McCain’s running-mate, amid mounting evidence that she has become a significant drag on the Republican ticket.

The Governor of Alaska spoke hours before giving a sworn deposition in the Troopergate inquiry in a hotel in St Louis, Missouri, as a second investigation opened into whether she abused her office by trying to have a state policeman fired to settle a personal score. A first report issued earlier this month concluded that she violated ethics laws in attempts to get her former brother-in-law sacked.

The revelation that the Republican National Committee spent $150,000 in September on clothes, hair and make-up for Mrs Palin and her family — undermining her image as an average “Hockey Mom” — was part of a set of broader problems facing her. New polls show that she has become a bigger liability for Mr McCain, 72, than any other factor.

A Wall Street Journal/NBC News poll on Wednesday asked voters what concerns them about the Republican ticket, and Mrs Palin was the No 1 worry for them; 47 per cent had a negative impression of her, while only 38 per cent saw her in a positive light.

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Her inexperience and faltering responses to foreign policy questions has also helped to erase the “Palin bounce” that boosted the ticket in the fortnight after she was chosen: 55 per cent now think that she is unqualified to be president, a troublesome number given Mr McCain’s age.

It also emerged that the highest-paid McCain staff member for the first two weeks of this month was Mrs Palin’s make-up artist. Amy Strozzi, who once did make-up work on the television show So You Think You Can Dance?, received $22,800 for that fortnight, more than the candidate’s chief foreign policy adviser.

In an interview with the Chicago Tribune, Mrs Palin said of the purchases at such exclusive shops as Saks Fifth Avenue and Neiman Marcus: “If people only knew how Todd [her husband] and I and our kids shop so frugally. My favourite shop is a consignment shop in Anchorage, Alaska, called Out of the Closet.”

She said of the controversy: “That whole thing is just bad! What did they say, 150 grand? It wasn’t anywhere near that. Those are not ours. We give those back, those go to charity or they’ll be auctioned off.” She added: “It’s kind of painful to be criticised for that, that is not who we are.”

Vice-presidential picks rarely have a significant impact on the outcome of presidential races, but Mrs Palin is emerging as an exception. While she has energised the conservative base — crucial for Mr McCain — she is also being cited as a major reason by some prominent Republicans for their defections to Barack Obama.

Colin Powell, President Bush’s former Secretary of State, said that her unreadiness to be president was a significant factor in his endorsement of the Democrat last week. Ken Adelman, a Republican hawk and former close friend of Dick Cheney who has become disillusioned with the Bush Administration, is backing Mr Obama. He said that the choice of Mrs Palin had made him switch sides.

Meanwhile a Republican election worker who claimed that a black man had carved a “B” into her cheek after seeing a McCain bumper sticker on her car has confessed that she invented the story. The McCain campaign was quick to denounce the alleged attack by an Obama supporter as “sick and disgusting”, and Mr Obama issued a statement deploring it.

Mr McCain and Mrs Palin telephoned Ashley Todd, 20, a white college student from Texas, expressing their concern. Last night Pittsburgh police arrested and charged her with making a false report.

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