CRUNCH talks are to be held over the proposed rail link to Glasgow Airport as concerns mount over the timetable for the project.

Amid ongoing claims the national transport agency is lukewarm over the contentious scheme, the heads of Renfrewshire and Glasgow councils will sit down with Scotland's new transport minister, Humza Yousaf MSP, to seek a definitive commitment on its delivery.

Mired in party politics, the rail link is the flagship project being promoted by west of Scotland councils as part of the £1billion-plus City Deal, with a new business case set to be submitted at the end of this year.

The Scottish and UK Governments, which fund the City Deal, have an veto the business cases for any section of the project if they believe the calculations are tenuous.

Ambitions for the link between Glasgow Airport and Central Station were dealt a recent blow after it was omitted from Network Rail's blueprint for the future enhancement of Scotland's trains network - a move its supporters described as "mind-boggling".

Ahead of the September 14 crunch meeting, Renfrewshire leader Cllr Mark Macmillan and Glasgow counterpart Cllr Frank McAveety have written to Mr Yousaf urging him to express firm support for the project.

But Mr Yousaf said the local authorities had yet to bring forward a feasible business case "which includes all costs and impacts associated with the project".

Renfrewshire Council leader Cllr Macmillan said the project must be recognised in a future masterplan for the rail network.

He said: “In order for this project to progress, the Minister’s transport agency Transport Scotland, needs to include it in future rail planning proposals due to be finalised next year. The project’s inclusion in this document is critical.

“Given the current economic climate and financial uncertainty, we must work together to address any outstanding issues and a firm commitment now from the Minister would send a clear signal of support for the country’s broader economic growth, increasing its global competitiveness and confirm that Scotland is open for business.”

Plans for a link from Glasgow Central to the airport originally secured the support of the Scottish Parliament in 2006.

But with spiralling costs, concern about management of the project and its business case and the fears over the impact of the squeeze on public finances, the SNP scrapped the plan in 2009."

The Glasgow Airport rail link was resurrected in 2014 after the announcement of the City Deal, an agreement between governments in Westminster and Edinburgh - as well as local authorities - to improve Glasgow infrastructure over the next two decades.

Mr Yousaf said: "Through the Glasgow City Region Deal, the Scottish Government has already made a significant commitment of £500 million funding over the lifetime of the deal.

“There is no question we want a solution to be found for the well understood access problems at the airport. I am surprised that the two councils have yet to bring forward a feasible business case which includes all costs and impacts associated with the project.

"We would expect to see any proposed project progressed in accordance with industry requirements. Given the continued challenging economic environment, it is crucial partners explore all options to help support Scotland’s economy.”

The meeting comes amid claims Transport Scotland is reluctant to include the project in its future rail planning proposals, the High Level Outlook Specification (HLOS), in turn raising concerns about how committed ministers are to the project. Consultation on the HLOS will start in October with a draft document expected in spring next year.

But Transport Scotland said "the progression or otherwise of any rail link to Glasgow Airport is not predicated by its inclusion in the HLOS".