How much longer can Wendy Alexander hold on?

Nationalists claimed Ms Alexander's credibility was "now in tatters" and she would never be able to recover enough authority to lead her party.

But angry Labour MSPs rallied to her defence, insisting there was "no question" of her resigning. However, Ms Alexander, who has endured almost a year of questions over her ability as leader, knows the punishment will hang over her all summer while the parliament is in recess.

She has already been criticised inside the party for her failure to land blows on Alex Salmond in the chamber and for her extraordinary decision to support an independence referendum.

This latest blow will only add to the sense within the party that Ms Alexander is very much on her last chance and that any further controversies will cost her the leadership.

One Labour source, who is not an MSP but a committed party activist, said he did not want her to stay on in the long term, but he did not believe she should go now as there was no-one lined up to take her place.

Others in the party were much more bullish, with her allies in the parliament claiming she had been the victim of an SNP witch-hunt and adamant there was "no question" of her standing down.

Ms Alexander was punished by the committee for failing to declare eight donations to her leadership campaign fund.

Every MSP has to declare any "gifts" of more than 540 in the register of members' interests within 30 days of receipt.

The eight donations, all for more than 540 but less than 1,000, were received by Ms Alexander's campaign team. She argued that she did not have to declare them because they were not "gifts" to her but donations to a political campaign that were held in bank accounts to which she did not have access.

She also stressed that she had approached the standards committee clerks and been told that she did not have to register the donations.

Ms Alexander's critics, however, claimed she had left it more than 30 days after receiving the first donations before approaching the committee clerks, which was a clear breach of the rules.

They were supported by Jim Dyer, the Standards Commissioner, who overruled the committee clerks and stated that Ms Alexander should, indeed, have declared the donations.

Because yesterday's committee decision took place on the last day of the parliamentary term, there was no time for the full parliament to vote on it. This means the suspension will hang over her for two months until the parliament reconvenes in the autumn.

Ms Alexander herself was unable to speak – she has lost her voice to laryngitis – but friends said she was furious with the committee's decision.

However, as SNP MSPs celebrated what they believed to have been a major blow against the Scottish Labour leader, it emerged the Nationalists may have trouble getting the suspension approved.

The punishment will have to be agreed by the whole parliament for it to take effect, and there was increasing evidence that Ms Alexander may win that vote when MSPs return at the start of September.

Last night, it appeared as if she could count on the support of the 46-strong Labour group, the 17 Conservatives and the independent Margo MacDonald when the issue goes to a vote.

This means that if either of the two Green MSPs or any of the 16 Liberal Democrats decide to back her too, she will have enough votes to see off the suspension threat.

The effect of the ban, if passed by MSPs, would be to exclude Ms Alexander from the half-day Wednesday session of the full parliament.

She would still be able to use the Holyrood complex and her pay would not be docked.

It is a largely symbolic punishment and it is the most lenient sanction the committee could have imposed.

But it will do Ms Alexander considerable damage if it is passed by the parliament and, even if it does not get through, the fact it will not be decided until September means she will be unable to make a fresh start following the donations scandal, until late in the autumn.

Labour MSPs were particularly angry last night because of the fact Ms Alexander had sought the advice of clerks to the standards committee and been told she did not need to declare the donations.

It was only when an SNP researcher made a formal complaint and the Standards Commissioner became involved that there was any different advice.

The Labour MSP David Whitton – speaking on behalf of Ms Alexander – said SNP politicians were out to have her "hung, drawn and quartered".

Asked if she accepted any wrongdoing, he said: "No she doesn't, because she sought advice, took advice, followed the advice – what more is she expected to do?"

He went on: "Wendy Alexander remains the leader of the Labour group and will still be the leader of the Labour group come September. We believe this is a politically motivated complaint by a member of staff of an SNP MSP – no member of the public has ever complained.

"We believe that, on the face of it, it is a politically motivated decision by the committee."

But the SNP MSP Roseanna Cunningham said: "Wendy Alexander and the Labour Party have been irreparably damaged by this protracted scandal. Her credibility is now in tatters, and it is unlikely ever to recover.

"From the start of this affair, Wendy Alexander has tried to dodge responsibility and spread the blame as widely as possible. A suspension from parliament is embarrassing for any MSP, even more so for a party leader."