First Minister Alex Salmond yesterday refused to give a firm commitment on when the M74 extension around Glasgow will finally take place.

Mr Salmond was pressed on the matter by Frank McAveety, the Labour MSP for Glasgow Shettleston, during First Minister's Questions at Holyrood.

Mr McAveety said the extension contract had to be finalised within 90 days - and claimed it was being held up because of "behind-closed-doors negotiations" between the SNP and the Greens, who oppose the project.

Earlier this week, The Herald revealed that senior Scottish Government officials were in talks with Interlink M74, the sole consortium to bid for the construction.

Mr McAveety said the proposed five-mile motorway extension, which is expected to cost between £375m and £500m, will be the country's most important infrastructure project over the next 10 years.

"Not just in economic growth but to make the Commonwealth Games, in your words, the best-ever," Mr McAveety told Mr Salmond.

And he asked: "Would he agree with me that this project is far too important to be left to sometimes behind-closed-doors negotiations with the Greens, and he should maintain his commitment to this development by ensuring that the contract is signed within 90 days?"

Mr Salmond called on Mr McAveety to produce evidence to support his claims and said it was arguable that other planned projects were of equal significance.

He said project was "huge", but added: "No-one surely in this chamber would suggest that value for money and proper considerations of tenders is something that should be overlooked in pursuit of completing a vitally important infrastructure project?"