Extra funding to deal with Scotland's ferry building scandal reached more than  £120m over a matter of months in the wake of further issues with completing long-delayed lifeline vessels, it can be revealed.

The Herald understands a new due diligence investigation will look at whether to sanction a request by the nationalised shipyard firm Ferguson Marine for extra costs which could rise to over £51m.

It comes just five months after the Scottish Government completed a previous eight-month long due diligence exercise which sanctioned an extra spend of £72m that the nationalised shipyard firm Ferguson Marine said was needed to complete the two lifeline vessels.

It has been confirmed that the new investigation will be for extra costs of at least £21m.

Further contingency costs have also to be considered which could add up to a further £30m to the bill.

READ MORE:  The 'missing' £128m in ScotGov's take on cost of ferries scandal

But it is understood there is a further potential multi-million pound bill expected after the vessels are handed over because equipment warranties have expired.

The Herald: Ferguson Marine and (inset) David Tydeman

It comes after David Tydeman, chief executive of Ferguson Marine said the safety regulator is at least in part to blame for delays in safety clearances for two vessels at the centre of Scotland's ferry fiasco which is estimated to have contributed to new cost rises due redesigns of emergency evacuation routes.

Capital costs of building Glen Sannox and Glen Rosa could now go over £400m - over four times the original £97m contract.

Wellbeing economy secretary Neil Gray confirmed in May that the government was to proceed with the ships after the earlier due diligence even though the project failed its value for money test.

He issued a rarely-used ministerial direction to overrule the value for money financial test saying completing the vessel at the nationalised yard was the fastest way of delivering more ferry capacity.

The review concluded in May that there was a value for money case for finishing the first vessel Glen Sannox but not for Hull 802.

Some £15m was given to the yard in advance of completing due diligence with the further £57m to be given this year.

A ferry user group official said that the extra costs were "mind-boggling" and that the cost increases in the year were set to eclipse the total cost of two ferries currently being built in Turkey.

Cemre Marin Endustri shipyard in Turkey was awarded a £115m contract to build two ferries for longsuffering islanders earlier this year as attempts are made to shore up the nation’s ageing ferry fleet. It won a £105m contract for two further ferries last year.

The Herald:

"The financial mess that has been caused by failings across the board in the building of these ferries that are desperately needed is quite staggering," he said. "It is no wonder that we are having to go to Turkey to have ferries constructed to support our lifeline services."

Official checks on the long-delayed Glen Sannox and Glen Rosa by the Maritime and Coastguard Agency (MCA), which is responsible for implementing British and international maritime law and safety policy, were rejected on June 1 this year sparking a redesign.

Mr Tydeman has 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 last month.

He said part of the problem was that local MCA officials in Glasgow had been "overruled" in relation to clearances by the head office in Southampton.

Among the issues to be resolved surrounded the installation of the evacuation routes on the ferries in order to satisfy the MCA.

The chief executive of the MCA said the safety rules relating to the vessels had been in place since 2009.

Ferguson Marine had originally indicated that it approached the safety body about the escape routes on April 11, 2023 and the plan was rejected sparking a redesign.

The issues related to requirements over additional protection to ladders and stairways as well as fire shelters and a means of escape from workshops within machinery spaces.

One of the key issues was a reliance of passengers exiting through areas dedicated to crew.

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

The two lifeline ferries were both due to hold up to 1000 passengers when they eventually come into service.

CalMac had expected Glen Sannox to be handed over in December 2023, and Glen Rosa in December 2024. They say that once handed over there will be a two month period where they will carry out crew familiarisation and network trials.

The Herald:

But the further work on the vessels from the Scottish Government-owned Ferguson Marine shipyard raised further fears that the Glen Sannox would not be available for the start of the 2024 summer season.

Mr Tydeman had previously stated he was optimistic that Glen Sannox should be available to passengers in spring 2024.

The delayed second vessel, Glen Rosa, which was supposed to be online in the last reschedule in the autumn of 2024 having already been delayed to the end of March 2024, had been pushed back to November, 2024. The contract backstop was stated as being at the end of December 2024.

Both vessels were due online in the first half of 2018, with both now to serve Arran, but are at least five years late, with costs expected to be quadruple the original £97m contract.

A Ferguson Marine (Port Glasgow) spokesman confirmed that it “will update the Net Zero, Energy and Transport Committee on design upgrade and other contingency costs in due course.”