Making a profit from what society has deemed to be criminal behaviour requiring incarceration is seen as ethically wrong

Academics' report

But the universities' report, compiled by Professor Christine Cooper and senior lecturer Phil Taylor, says the firm has "hugely inflated" the cost of new prisons being funded solely by the taxpayer.

It argues that if prison populations fall - as ministers insist will be the case - the private option is likely to be very costly.

"Making a profit from what society has deemed to be criminal behaviour requiring incarceration is seen as ethically wrong," it goes on.

Officers are threatening action

"PricewaterhouseCoopers is non-neutral, or biased, in the sense that they were paid by the Scottish Executive to 'support investment decisions that form part of the Estates Review.'"

A Scottish Executive spokesman responded: "We will consider this report as part of the ongoing consultation process.

"The executive stands by the work carried out by the Scottish Prison Service and the expert analysis carried out by PricewaterhouseCoopers."

'Devastating blow'

The academics' report is likely to form the centrepiece of a debate later this week at the Scottish TUC as unions step up their pressure on the executive to reduce their dependency on public private partnerships.

As well as the three new private jails, there are plans to close Peterhead jail and Low Moss prison, near Bishopbriggs in Dunbartonshire.

Jim Wallace: Faces opposition

Prison officers have condemned the decision taken by the Justice Minister Jim Wallace and have been drawing up plans to oppose the private jails.

They say the move would mean a third of prisoners in Scotland being housed by the private sector - a higher proportion than almost anywhere else in the world.

There have been warnings of industrial action if the executive presses ahead with the policy.

Officers also point to the sometimes troubled history of Kilmarnock, Scotland's only private jail in operation so far.

Alex Neil, an SNP regional MSP for Central Scotland, said the report was a "devastating blow" for the executive's prison privatisation plans.

• Meanwhile, a petition signed by almost 200 prisoners calling for Peterhead to be retained has been presented to Mr Wallace.

  Banff and Buchan MSP Stewart Stevenson said it undermined the executive's claim that the prisoners would be better off nearer their families in the Central Belt.