Douglas Fraser: "Some send their poison by post. Others post it online"

Wendy Alexander, Scottish Labour's embattled leader, has suffered another blow after it emerged a top aide is to quit.

Although Labour officials were last night stressing Tony McElroy had been planning his departure for a while, the timing could hardly be worse for the party's leader.

He will be the third spin doctor to leave since Ms Alexander became leader less than five months ago, and news of his departure comes as the Electoral Commission prepares to announce whether they are calling in the police over the illegal donation to Ms Alexander's leadership campaign.

Mr McElroy, who has been Scottish Labour's head of communications for the past four-and-a-half years, is leaving to take up a public affairs post with the supermarket giant Tesco.

His departure follows that of Brian Lironi, who resigned as Labour's chief spin doctor at Holyrood after Ms Alexander became leader last September.

Matthew Marr was also forced to resign as Ms Alexander's spokesman in November after shouting an obscenity at First Minister Alex Salmond during The Herald Politician of the Year awards ceremony. One senior Labour source last night predicted that other disgruntled party workers are set to resign.

The commission is meeting tomorrow and is expected to announce the outcome of its two-month investigation into the illegal donation the follow-ing day.

Ms Alexander has admitted accepting the £950 cheque from Jersey-based businessman Paul Green, despite the fact non-UK residents are banned from making political donations.

Dr Jim Dyer, the Scottish Parliament's Standards Commissioner, has already called in the procurator-fiscal over Ms Alexander's failure to register donations to her campaign fund.

Her defence is that she had sought and followed guidance from parliamentary authorities in November that she did not have to declare the money.

When asked yesterday if she was considering resigning in light of the new developments, Ms Alexander said: "I don't think anybody's future should be called into question on the basis of following the advice of parliamentary authorities."

But yesterday a parliament spokeswoman said: "While we cannot comment on any individual case which may or may not be under investigation, we have no reason to believe that any member has been provided with erroneous advice from officials."

Dr Dyer issued a statement yesterday insisting he had no option but to refer Ms Alexander's case to the procurator- fiscal once he believed the rules had been broken.

He said: "I am not a final arbiter of what should be counted as a registrable interest - that is, in the end, a matter for the parliament and in some cases the courts."

A former deputy leader of the SNP also waded into the row by claiming Dr Dyer owed Ms Alexander an apology.

Jim Sillars said: "If I had been in Wendy Alexander's shoes this weekend, I would have sought judicial review of the administrative process and actions taken by the office, and person, of the Standards Commissioner in relation to this decision to make a referral to the procurator-fiscal."