Scotland's ferry-building fiasco has cost the public more than £1.3m a week since the Scottish Government took control of the shipyard at the centre of the scandal just over four years ago, the Herald can reveal.

The latest capital costs of the two wildly delayed and over-budget ferries being built at nationalised Ferguson Marine - which do not include Scottish Government budget payments for running costs and salaries - are currently estimated to be at £425.5m, nearly four-and-a-half times the original £97m contract cost.

It can be revealed that the extra costs to complete the ferries since nationalisation has rocketed by £297.3m.

It has risen by a further £185m since the Scottish Government-appointed turnaround director Tim Hair estimated it would cost £112.3m to finally complete Glen Sannox and Glen Rosa immediately after Ferguson Marine was nationalised in December, 2019.

Just over two years later Ferguson Marine chief executive David Tydeman, in his first analysis after taking over from Mr Hair on February 1, 2022 put the further post-nationalisation costs up by £8.2m from the Tim Hair calculation at around £120.5m.

READ MORE: Official auditors refuse to carry out Scots ferry fiasco contract probe

The soaring post-nationalisation costs have come after £128.25m was ploughed into the project when the yard was under the leadership of tycoon Jim McColl.

Since September last year, when it was estimated the extra post nationalisation costs would be £269m it has gone up again by around £28m.

In his latest estimate, Mr Tydeman has set a ceiling of £150m for the delivery of Glen Rosa and believes Glen Sannox will be complete at around £147.3m. He has stated he hopes to bring the cost of Glen Rosa down to below £140m.

The two ferries being built at the Inverclyde shipyard were due online in the first half of 2018, with one initially to serve Arran and the other to serve the Skye triangle routes to North Uist and Harris, but are at least six years late. It has been confirmed that both are now to serve Arran.

The Herald: Glen Sannox finally sailed on its 'own steam' during sea trials two weeks ago and is still subject to delays and cost rises.

Glen Sannox, was launched by Nicola Sturgeon nearly seven years ago and is not expected to be ready for passengers till August at the earliest.

Glen Rosa was meant to be delivered to CalMac in August 2018, but that is currently scheduled to be completed in May 2025 - meaning it would be ready for passengers the following August.

The dates of arrival and the costs have been in a constant state of flux as their construction has been plagued by design challenges, cost overruns and delays.

In the midst of the delays and soaring costs, Ferguson Marine under the control of tycoon Jim McColl fell into administration and was nationalised at the end of 2019 with state-owned ferry owners and procurers Caledonian Maritime Assets Limited (CMAL) and the yard's management blaming each other.

A ferry user group official said that the extent of the issues with the ferries had been clearly been underestimated from the first day of the Scottish Government takeover.

"The blame game on who was responsible is one thing but the Scottish Government was supposed to turn this around, hence the turnaround director, but we have never come close to getting the costs or the dates of arrival for these ferries right and it has been under Scottish Government control for over four years. The wanton mismanagement of this project remains something I can scarcely believe and the costs are staggering."

The new wellbeing economy secretary has said that the latest cost increases and delays to delivery dates were "extremely disappointing".The Herald: Mairi McAllan

Her predecessor Neil Gray had made similar comments on previous cost rises and repeated impressed on the chief executive that further delays and cost increases would be "inexcusable and profoundly frustrating".

READ MORE: Ferguson Marine's vital bid for new ferries to be more pricey than rivals

She is planning an "urgent conversation" with the chairman of Ferguson Marine, Andrew Miller to agree next steps and set out "my very clear expectations" about future governance.

Scottish Conservatives' shadow transport minister Graham Simpson said the ferries "have to be the worst value for money of anything in public procurement history".

He added: "A succession of SNP ministers has expressed disappointment with the cost increases but they never act to stop it. There has been a blank cheque for these ferries since day one.

"The latest minister to be in charge of this scandal says the delays and cost increases are inexcusable. Fortunately for her we appear to be near the end of the building of these two vessels so she might be the lucky one to see them go into service."

Mr Tydeman in his latest update said that there has been "significant re-work" on Glen Sannox on what he called "legacy issues and design and construction errors in the early stages" with pre-nationalisation Ferguson Marine and then since the Scottish Government took over."

Among the issues with both vessels involved safety clearance failures last June which led to a redesign and the installation of new evacuation routes in order to satisfy the Maritime and Coastguard Agency (MCA), which is responsible for implementing British and international maritime law and safety policy.

Mr Tydeman admitted he knew about the problems within three months of him joining the firm in February, 2022. But the issues did not become public knowledge until September, 2023.

The Herald: Ferguson Marine and (inset) David Tydeman

The changes mean the two vessels will carry nearly 300 passengers fewer than contracted for to allow for improved passenger seating layouts.

The two lifeline ferries Glen Sannox and Glen Rosa were both due to hold up to 1000 passengers when they eventually come into services.

There have also been issues with the engine systems as Ferguson Marine struggled to find a company to install the so called green LNG technology needed for it to be environmentally-friendly. It will run on diesel until this is sorted.

"Our aim is to avoid all such re-work on the second ship...," he said. "We have had more opportunity to build [Glen Rosa] differently and the strategy of deferring the outfitting work until we have finished the build of Glen Sannox creates the scope to avoid the extensive re-work encountered on Glen Sannox.

"Consistently over the past 18 months, we have set out that Glen Sannox has been a complex design and engineering challenge made harder by many legacy issues with the past, administration, and pandemic impacts.

"We have also set out that [Glen Rosa] will be a delivery challenge, well planned, with contractors engaged and the opportunity to complete the build more efficiently."

A Scottish Government spokesman said: "Officials have started due diligence on the latest projections to ensure they are accurate and robust and the Wellbeing Economy Secretary will update Parliament once this work is complete.

“The Scottish Government’s priorities have always been the completion of the two ferries, securing a sustainable future for the yard and its workers, and supporting our island communities that rely on this type of vessel.”