Further delays are expected in the completion of the two ferries at the centre of Scotland's ferry fiasco after safety regulators demanded new design changes before any approvals are given.

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.

The work means planned sea trials of the Glen Sannox have been delayed until the first quarter of next year.

CalMac had expected Glen Sannox to be handed over in December 2023, and Hull 802 in December 2024. They say that once handed over there will be a two month period where we will carry out crew familiarisation and network trials.

The latest update 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.

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More details of the impact of the changes, including any cost implications are due to be given next month.

David Tydeman, chief executive of the nationalised Inverclyde shipyard firm had previously stated he was optimistic that Glen Sannox should be available to passengers in spring 2024.

The delayed second vessel, only known as Hull 802 which 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.

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Both vessels were due online in the first half of 2018, with one intitially to serve Arran and the other to serve the Skye triangle routes to North Uist and Harris, but are at least five years late, with costs expected to be quadruple the original £97m contract. It has been confirmed that both are now to serve Arran.

Mr Tydeman said: "The MCA have reassessed the application of 'cargo ship' rules to the crew spaces of passenger ferries (on a broader basis than just Ferguson and Glen Sannox/802) and for the last two months we have been working to close the impacts of this and some other approvals issues.

"We have been designing and planning the necessary modificiations to some doorways in crew corridors and three additional staircases between decks 5,6 and 7. We have one issue to finalise and hope to reach final agreement with the MCA within the next two weeks so that we can carry out all the modifications before Glen Sannox moves to the dry-dock just before Xmas."

He added: "This means the sea trials will move into the first quarter of the new year and the commissioning of the liquefied natural gas system at Troon (which must be done after dry docking) will also be moved to after Christmas".

It comes after ministers were accused of wasting millions over major changes to plans for the launch of vessels.

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."