Labour attempts to play down the row over PFI during STUC week were blown apart yesterday when a leading academic accused Health Minister Andy Kerr of "malicious slander".

Jack McConnell yesterday received a polite but cool response inside the main hall at congress, while the SNP's Nicola Sturgeon was well received in the conference area outside. But the embarrassingly wafer-thin majority by which the general council of the STUC voted to endorse Labour on Monday night will come back to the floor of congress today and some unions are already mounting a challenge to that decision.

Mr McConnell mounted a fierce assault on the SNP, and in particular its planned local income tax replacement for the council tax, saying: "Mark my words - the SNP's local income tax is the poll tax mark two." He also said the SNP's values led to "grievance, conflict and discord".

Ms Sturgeon, asked by one delegate: "So you didn't get in to the hall then?", replied: "No, we'll leave that till next year when we're in government."

Ms Sturgeon focussed on public services and her party's alternative to private finance schemes. She insisted: "PFI/PPP means credit card levels of annual interest repayment. I have no doubt we can do better with public assets delivered through a not-for-profit trust." The SNP, which is now attracting union endorsements and donations from the likes of the Fire Brigades Union, feels the tide is turning. Ms Sturgeon's visit to the STUC in Glasgow came at a time of unprecedented turmoil within the movement over its political links.

That will be accentuated by the latest contribution from Professor Allyson Pollock of the Edinburgh University Centre for Public Health Policy, who in a letter to The Herald today confronts Health Minister Andy Kerr: "To call us biased academics who seek to mislead the public is a malicious slander. It also constitutes an unnecessary impoverishment of public debate."

Professor Pollock says she would welcome a real argument based on published figures, but for as long as ministers refuse to allow access to supposed "value for money" comparisons she is sceptical.

PFI was in issue which was to the fore at the STUC in Glasgow yesterday. Ms Sturgeon said: "It's time for a better value alternative to the costly PFI/PPP. In communities across Scotland we see the real cost of Labour's privatisation agenda, with the loss of vital local health services the unacceptable price Scots are being asked to pay. Our new approach will put people before profiteering and communities before centralisation.

"PFI/PPP means credit card levels of annual interest repayment. I have no doubt we can do better with public assets delivered through a not-for-profit trust. That's why we will bring forward plans for a Scottish Futures Trust. This will offer better value finance through bond issue and, I believe, over time crowd out the costly PFI/PPP."

Both Labour and the Liberal Democrats jumped on the SNP's PFI policy yesterday.

Tavish Scott, the LibDem campaign director, said: "This is a massive U-turn from the SNP. For the last eight years they have opposed building new schools and hospitals using PPP. Now, when the pressure is on, they are trying to wriggle away from their commitment." The SNP insisted that they had always made clear they would have no powers to cancel or direct contracts.