Scottish Government officials privately admitted they made the "wrong call" over a major funding announcement for Glasgow made in the build-up to last month's council elections.
The £8.35 million city centre office refurbishment was made public just before the vote as the SNP targeted the capture of Glasgow City Council from Labour. The Nationalists went onto to win the city after generations of Labour rule.
Opponents claimed the announcement breached "purdah" rules which prevents major Government announcements in the build-up to elections which could be seen to sway the outcome in favour of the governing party.
The Scottish Government top civil servant, Permanent Secretary Leslie Evans, publicly declared no guidance had been broken after concerns were raised.
But correspondence between officials at St Andrews House obtained through Freedom of Information by the Conservatives paints a different picture. A probe into the episode was ordered by Ms Evans which found that communications and policy officials had been aware of purdah guidance.
"These decisions are ultimately a judgement call and it is clear on this occasion the wrong call was made," states the report by Shirley Laing, Deputy Director in the Social Justice and regeneration Division.
In another email, Lesley Fraser, director of Housing and Social Justice at the Scottish Government states that one of her officials was "apologetic for not having questioned this further."
"My apologies to you and the Perm Sec, Sarah," states the email to Sarah Davidson, director general of communities.
"I think this has been a genuine error of judgement about regular announcements that affect communities across Scotland - but clearly the wrong call on this occasion."
But another official, James Hynd, Head of Cabinet, Parliament and Governance Division then intervened to clarify what "error of judgement" means.
This prompts further exchanges before Mr Hynd tells the Permanent Secretary that the issue was down to a "process failure. " He went onto draft the official letter from Ms Evans to Tory MSP Ross Thomson which stated that "no guidance was broken."
The Tories today called for a probe into the "cash for votes" affair.
Mr Thomson said: “After we pressed them, Nicola Sturgeon’s top official tried to claim in public that the government had done nothing wrong.
“Now we know the truth – officials admitted they made ‘the wrong call’, and then the SNP government tried to cover it up.
“Nicola Sturgeon must now launch a full investigation into this entire murky affair."
Scottish Labour General Election campaign manager James Kelly said: "This is a damning revelation, and demands an urgent response from Nicola Sturgeon. She cannot bury her head in the sand any longer. There must be a full and frank investigation into how this announcement came about."
A Scottish Government spokeswoman insisted that the “error in judgement” referred to the failures to consult more senior officials and that no rules were broken.
“As the Permanent Secretary has already made clear, following an inquiry into the funding announcement, there is no evidence to suggest any breach of pre-election guidance,” she said.
“Our election guidance states that where there is any doubt about the application of the guidance, the matter should be referred to senior staff for consideration. No such upward referral took place on this occasion, which was an error of judgement. This was a lapse in the internal handling but not a breach of the rules.”