A LIBERAL Democrat MSP who voted to suspend Wendy Alexander from Holyrood says he will resign his post if the Scottish Parliament does not back his committee's decision.

Hugh O'Donnell, whose vote was crucial in delivering a fatal blow to Alexander's leadership, says MSPs will "undermine" the Standards Committee if they overturn the proposed ban after a debate scheduled for Thursday.

MSPs could vote down the one-day suspension plan on the grounds that Alexander - described yesterday by Chancellor Alistair Darling as "not likeable at all" - has suffered enough by resigning.

Alexander, the MSP for Paisley North, quit as Scottish Labour leader in June after the Standards Committee found she had broken Holyrood rules by not declaring around £10,000 in leadership campaign donations.

The committee endorsed a report by the Standards Commissioner, Jim Dyer, who also concluded that she had fallen foul of the rules, and recommended a one-day suspension from parliament.

However, the committee was divided, with the recommended ban being pushed through on a four-three vote.

The three Nationalists on the committee voted for the move, as did LibDem O'Donnell, with Conservative MSP Jamie McGrigor and the two Labour members opposing suspension.

The full parliament will debate and vote on the committee's proposal this week, and several non-Labour MSPs believe the ban will be voted down.

But O'Donnell said a rejection would put his colleagues in a difficult situation: "I am very clear. The recommendation of the committee to the parliament merits the support of the parliament. If the parliament does not support the recommendation, it calls into question the tenability of the position of myself and the other committee members who voted to take the action."

He said he would quit the Standards Committee if MSPs overturn its recommendation of suspension, saying: "I would find it almost impossible to stay on the committee. If the parliament does not support the recommendation, at the end of business on the day of the vote I will raise a point of order and resign from the committee on the floor of the chamber."

O'Donnell added: "If our judgment is not supported by the parliament, on what basis do we investigate anyone else?"

Asked if he agreed with Wendy Alexander when she claimed to have been the victim of a partisan decision, he said: "It's a smokescreen in my view. The reality is that the group around her very clearly set the thresholds for donations at a level that would avoid individual identification of donors.

"I just did not understand why they did that. It made no sense whatsoever."

With Labour MSPs certain to vote against suspension, and Nationalist members expected to support the plan, the votes of the smaller parties will be crucial.

The Sunday Herald understands Conservative MSPs are generally sympathetic to Alexander, while the LibDems are said to be split.

The two Green MSPs are not thought to have made up their minds on the issue, while Independent Lothians MSP Margo MacDonald is expected to back the former Labour leader.

Meanwhile, Darling used an interview with the Guardian yesterday to criticise Alexander's personal manner, describing her as "not likable at all".

However, it emerged the Chancellor called Alexander yesterday to apologise and said he had the "utmost admiration and respect" for her.