The latest scheme to build a multi-million-pound link to Glasgow Airport has hit the buffers after experts warned it would do more economic harm than good.

Local and national government officials last year threw their weight behind a £144m tram-train connection from Central Station to Abbotsinch.

The scheme was a cut-price alternative to the Glasgow Airport Rail Link or GARL axed by the Scottish Government nearly a decade ago amid grave concerns over its value for money.

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READ MORE: ANALYSIS: End of the line? 

However, now consultants hired to review the business case for the new link have queried both the proposed costs - and benefits - of the new scheme.

Experts from Jacobs stress the latest design of the link - which would see vehicles run along heavy rail to Paisley and then a new light spur to the airport - would clog up rail networks south of the city.

In a report prepared for the Scottish Government quango Transport Scotland, they suggest trains full of hundreds of commuters from Ayrshire and Inverclyde be would slowed by two and a half minutes to make away for trams carrying far fewer airport passengers.

That modest sounding delay, they added, was would cost the economy £4m a year alone.

Cuttingly, Jacobs experts note that the economic disadvantages of a slower, less reliable service from key commuter areas had not been examined by the council officials who came up with the current business case.

They concluded: “Such an increase may also result in economic dis-benefits to the Ayrshire and Inverclyde region. This issue has not been considered by the Project Team.”

The railway between Glasgow and Paisley was upgraded from two tracks to three - partly to provide for extra capacity for the old GARL scheme.

READ MORE: ANALYSIS: End of the line? 

But a rise in popularity for train travel means all that additional capacity has been used up.

The tram train scheme - dubbed the Glasgow Airport Access Project or GAAP - would also put huge pressure on capacity at Central Station, said Jacobs.

Small tram train would take up as many platform slots as long commuter trains, they said. Projects jeopardised by GAAP would include plans to electrify services to and from East Kilbride.

Jacobs estimates that many passengers - such as those going to Queen street station - would still be faster on the existing bus service than on GAAP. And, like successive experts before them, they stress that a simple A to B journey from Central Station to Abbotsinch would not take many people off roads. Most passengers, after all, are not going from the city centre to the airport. The GAAP link, moreover, would not get anyone to the airport in time for many early flights.

The new link was to have been funded by the City Deal, a roughly £1bn pot for investment from the UK and Scottish Governments.

The City Region cabinet - the panel of council leaders hoping to spend that cash - now look set to go back to the drawing board on the rail link.

Glasgow leader Susan Aitken, who chairs the cabinet, signalled that local leaders were ready for a rethink.

She said: “We remain committed to a surface access project to Glasgow Airport, funded from the City Deal.

“However, it is crucial that we fully explore the limitations and risks this report states the GAAP project in its current form could face.

“The report has cast up a number of areas of concern around the tram-train scheme which may lead us to revise the strategic business case to ensure the project we commit to is equipped to lever the economic growth and other social and environmental benefits it has the potential to.

“I am confident this can be done without adding substantially to delivery timescales.

She added: “The findings of this study provide the foundations for Glasgow and partner authorities to better deliver the long term aspiration for improved connectivity to Glasgow Airport not put an end to it.

“We will consider the findings and discuss them with partners in the City Region Cabinet, as well as Network Rail and Transport Scotland, in the coming weeks.”