SEA trials for a much-delayed and over-budget ferry have been held up due to last-minute changes, the Ferguson Marine shipyard has said.

CalMac had expected Glen Sannox - the first of two ferries being built at the government-owned shipyard - to be handed over in December 2023, and Hull 802 in December 2024.

The latest update from Ferguson Marine has raised further fears that the Glen Sannox will not be available for the start of the 2024 summer season.

In a further update this week, David Tydeman said the Maritime and Coastguard Agency had “re-assessed the application of ‘cargo ship’ rules”, meaning internal changes had to be made to the vessel.

Among the issues to be resolved is the installation of additional staircases on Glen Sannox and Hull 802 in order to satisfy the Maritime and Coastguard Agency (MCA), which is responsible for implementing British and international maritime law and safety policy.

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“This will mean that sea trials will move into the first quarter of the new year and the commissioning of LNG (liquified natural gas) systems at Troon (which must be done after dry-docking) will also move to after Christmas,” Tydeman said in a letter to Holyrood’s Net Zero, Energy and Transport Committee on Tuesday.

“We now meet weekly with key individuals from the Scottish Government, Transport Scotland, CMAL and CalMac to jointly monitor the commissioning, trials and handover programme, and how this best works with the subsequent mobilisation of crew and the start of CalMac’s passenger operations.”

Tydeman stopped short of confirming the changes will impact on the expected delivery date, saying instead an update on costs and handover will be given at the end of next month.

The yard was rescued from collapse in 2019, unmasking extensive issues with the two vessels and sparking two parliamentary inquiries and an Audit Scotland investigation.

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The ferries, which will serve islands of Scotland’s west coast, were due to be in service in 2018 at a price of £97 million, but delays have led to spiralling costs which could amount to more than three times that figure.

A ferry user group official said that the news was the "latest in a long line of problems that have turned the construction of the ferries even after nationalisation into an unfunny joke".

"Islanders will just be thinking, just get on with it," he said. "But nothing can happen about these ferries until they are signed off by the MCA and right now it remains an issue."

Earlier this year, Wellbeing Economy Secretary Neil Gray was forced to give a ministerial direction for work on the as-yet-unnamed hull 802 to continue, after advice found it would not be “value for money”.