THE Scottish Government has declared it will not sanction any further funding towards the soaring cost of completing the two ferries at Ferguson's until 'due diligence' is carried out.

Deputy First Minister John Swinney issued the statement after the boss of the Port Glasgow shipyard informed MSPs that a further £84m was needed to deliver the two vessels into service.

The Telegraph told last week how the cost to taxpayers for the flawed venture has now reached a staggering £338m.

Mr Swinney said: "Our priority is to undertake our own due diligence and this will be supported by external, independent financial advisors to ensure a rigorous approach is taken to scrutinising this request for additional funding.

"Let me be clear that no decision on any potential further investment has yet been made, and will not be made until this work has been completed.

"We are fully committed to financial transparency and I will update the Scottish Parliament in due course."

Greenock-born Conservative MSP Jamie Greene has hit out at the latest twists in the saga, in the wake of a BBC documentary suggesting the award of the original £97m dual-fuel vessels contract to Ferguson's was rigged.

Mr Greene said: "Our island communities deserve so much better than the scandal that has surrounded their lifeline ferry services.

"The SNP promised in 2012 that there would always be sufficient capacity on routes to meet demand, but today islanders find connectivity in an even more dire state than it was ten years ago.

"Our islands need new ferries and they need them now, but this new revelation means they will now have to wait even longer than they were previously promised.

"We need real political leadership, but right now we have very little of that here in Scotland — that needs to change sooner rather than later."

In a letter to MSPs, Ferguson's chief executive Mr Tydeman confirmed that completion costs for Glen Sannox now stand at £101m, while the price of her sister, Hull 802, is currently £108.6m.

It means that the build cost under nationalisation is £209.6m — up by £84m since March.

However, when £83.3m of 'milestone' payments made to the yard when it was owned by business tycoon Jim McColl, plus £45m of Scottish Government loans are taken into consideration, the total bill to taxpayers has reached £338m.

Mr Swinney said: "Following the company's recent board meeting, Ferguson Marine chief executive officer David Tydeman has set out proposals relating to the cost estimates and timetable for delivering vessels 801 and 802.

"He has confirmed the target for completion of Glen Sannox remains April-May 2023, with liquefied natural gas commissioning in May 2023."

The Deputy First Minister added: "The Scottish Government remains committed to a sustainable future for the shipyard and supporting the island communities which rely on this type of vessel, while safeguarding the hundreds of jobs for workers on the Clyde and the apprentices that are now beginning a career in shipbuilding at Ferguson Marine."