Sarah Palin’s lawyers were accused yesterday of trying to delay a potentially damaging inquiry into the Republican vice-presidential nominee until after the general election.

The allegations came after a key witness in the Alaskan Troopergate investigation – an official inquiry into whether Mrs Palin abused her office as state governor – refused to be interviewed under oath on the advice of Mrs Palin’s private lawyer.

The ethics investigation, being conducted by a bipartisan group of Alaskan state legislators, is looking into an accusation that Mrs Palin orchestrated a campaign to pressure the Alaskan police chief into firing her former brother-in-law, a state trooper who had been involved in an ugly divorce from Mrs Palin’s sister. The commissioner, Walt Monegan, refused to sack the trooper, Mike Wooten, and was later fired by Mrs Palin. He alleges that he was dismissed for “my unwillingness to take special action against her former brother-in-law”. Mrs Palin, who has denied any wrongdoing, said that Mr Monegan was fired because of disagreements over the budget.

When Mr Monegan first went public with his allegation, Mrs Palin denied that she or any of her staff had taken any action to try to persuade Mr Monegan to fire Mr Wooten. The trooper was briefly suspended in 2005 for using a Taser gun on his ten-year-old stepson and for shooting a moose illegally. Yet earlier this month Mrs Palin was forced to admit that half a dozen members of her administration had made more than two dozen calls to state officials on the matter – but that she was not aware of the communications.

One of the calls concerning Mr Wooten was from Frank Bailey, one of Mrs Palin’s chief aides. He is the witness who refused to give a statement to investigators. Earlier this month Mrs Palin released an audio recording of a call Mr Bailey made to a state official about Mr Wooten, in which Mr Bailey says: “Todd and Sarah are scratching their heads, ‘Why on earth hasn’t this, why is this guy still representing the [police] department?’ He’s a horrible recruiting tool, you know.” He adds: “The Palins can’t figure out why nothing’s going on.”

Mrs Palin has placed Mr Bailey on administrative leave. She says that he was not speaking on her behalf – and did so without her knowledge – and Mr Bailey has said the same.

Hollis French, a Democratic state senator leading the ethics investigation, accused Mrs Palin’s lawyers of using stalling tactics to delay the final report, which had been due to come out on October 31 – five days before the election.

Mrs Palin’s lawyer, Thomas Van Flein, is challenging the state legislature’s jurisdiction to investigate whether she abused her gubernatorial powers to settle a personal score. He says that the state personnel board should be handling the matter.

Mr French told theAnchorage Daily News: “This will certainly not help [us] get this work done on time.” In another interview with ABC News, he said that the report was “likely to be damaging to the governor’s administration. The governor first issued a blanket denial but now she’s had to back down and that’s a problem. She has a credibility problem.”

A spokesman for John McCain, the Republican nominee, said that the lawyer’s decision to challenge the jurisdiction of the ethics investigation had nothing to do with Mrs Palin or the campaign. Mr Van Flein said: “I am making the legal strategy for the governor. We conduct our own strategy internally. I am not working for the McCain campaign and they are not working for me.”

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