AROUND £35 million has been shelled out in the last 18 months to fix serious design flaws on just one of the already over-budget and years-late ferries being built in Port Glasgow.

Ferguson Marine chief executive, David Tydeman, revealed the staggering figure to MSPs today as he admitted that 'lots of mistakes' have been made in the construction of the Glen Sannox and Glen Rosa CalMac vessels.

Mr Tydeman said the two ships - expected to cost around £400m to finish, almost four times the original budget - have proven more complex to build than a Royal Navy Type 26 frigate.

And the CEO said that he is now 'more confident in the pricing than the delivery dates' for the ferries - with Glen Sannox due to be handed over in March next year and Glen Rosa scheduled for delivery in May 2025.

Addressing the Scottish Parliament's net zero, energy and transport committee this morning (Tuesday), Mr Tydeman said: "In the first few months after being appointed CEO of Ferguson Marine in February 2022 it became very clear to me that the design was far from complete for Glen Sannox and much re-work and re-design would be required.

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"Less than five per cent of cabling and only 20 per cent of pipe spools had been installed at that time.

"Regrettably we've encountered many more problems than I'd first imagined and the amount of work to solve design clashes and errors of the past has been significant.

"I estimate that over 50 per cent - about £35 million - of the increases over the last 18 months on Glen Sannox have come directly from re-working the design, sometimes regrettably involving two or three iterations."

Mr Tydeman, who was joined at the Holyrood hearing by Ferguson Marine chairman Andrew Miller, said that the design challenges have been 'very substantial' due to numerous errors made by predecessors.

Listing 'one of many examples', Mr Tydeman said that hydraulic pipework for the control systems opening the clamshell doors on Glen Sannox had to be removed and re-done after it was installed in mild steel instead of stainless steel.

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He added: "Only about 10,000m of cabling was in place in the ship in February 2022; we now have 310,000m of cabling installed, all of that has gone in in the last 18 months.

"Overall, combining the £123m incurred by FMEL between 2015 and 2019 and the latest forecasts I've set out, Glen Sannox will have cost just over £200m to complete, while Glen Rosa is expected to be £40m less, reflecting the benefit of being the second ship."

The Ferguson Marine boss said that in his estimate, the cost of each ship should have been around £70m - but he confirmed that the yard is 'making steady progress' on Glen Sannox and he is hopeful of being able to 'stay within the budget and contingencies' for Glen Rosa.

However, he warned of a potential 'cascade effect' if trials for Glen Sannox cause delays to the scheduled delivery dates for both vessels, while stating that, in his personal opinion, the impact of Covid on the progress of construction has previously been underestimated.

Earlier this month, an independent investigation found 'no evidence' of fraud in the awarding of the ferries contract in 2015.