The four plots at 57 Clark Street in Paisley were sold to Airlink Group, whose subsidiary company originally owned the land, in a private transaction after they failed to achieve the reserve price at auction in Edinburgh, The Herald can reveal.
The three-acre site next to the Paisley St James railway station, nicknamed the "Paisley triangle", comprises the last of 13 plots of land sold by the Scottish Government since the £210 million Garl project was axed four years ago.
It went under the hammer at SVA auction house in Edinburgh on June 26 with a guide price of £50,000, but failed to sell. However, The Herald understands it was bought immediately afterwards for £50,000 after representatives from Airlink Group approached the auctioneers with an offer for a private sale.
A spokesman for SVA confirmed that the purchase had been completed in late July.
The deal means the Scottish Government recouped just 6% of what it paid to acquire the site in May 2008, while Airlink Group - whose Glasgow headquarters were officially opened by First Minister Alex Salmond in February last year - has profited by at least £790,000 from the public purse.
According to records held by Registers of Scotland, the plot was sold in February 2008 by Airlink Security Park Ltd, the car parking subsidiary of Airlink Group, to SPT - the agency in charge of Garl at the time - for £840,125.
Businesses forced to relocate were also paid substantial compensation by taxpayers before the Garl project was scrapped in September 2009.
Since buying back the land, Airlink has turned it back into a car park. The Herald previously reported that governments are obliged to dispose of land bought through compulsory purchase powers which is no longer required, with previous owners offered first refusal.
The eight other Garl plots were sold off between 2011 and last year.
However, critics have accused the Scottish Government of offloading the sites to prevent an airport rail project being revived.
It comes a week after The Herald reported that the progress of an independent consultation on transport solutions for Glasgow Airport had stalled after Transport Scotland bosses became nervous about the inclusion of an airport-city rail link among a shortlist in April.
Councillor Gordon Matheson, leader of Glasgow City Council, said: "The Scottish Government is hell bent on sabotaging attempts to revive plans for a rail link to Glasgow Airport. They seriously miscalled the decision to cancel Garl in 2009, and this latest underhand attempt to hive off the required land has more to do with an assessment of their party political interests, than the economy of west central Scotland. "
James Kelly, Shadow Cabinet Secretary for Infrastructure, said: "This is a shocking waste of public money. It further highlights the own goal of the SNP government in cancelling the Garl project."
Halting the branch line element of Garl saved around £176m, said a Transport Scotland spokesman. He added that the "area has benefited from around £230m in rail infrastructure improvements alongside a new £430m fleet of Class 380 trains" on nearby lines.
Airlink declined to comment.