The main Arran ferry - which has been out of action since February - may not return to service until next March, CalMac has confirmed.

The ferry usually operates on the Ardrossan-Brodick route, but it was taken out of service earlier this year when significant repairs had to be carried out.

CalMac said new problems had been uncovered on MV Caledonian Isles while the ship was in dry dock.

No new date has been confirmed yet for its return to service, but the ferry operator warned that in a worst-case scenario it could miss the entire winter season.

It was originally due to return to service in September but a new gearbox fault was detected, which knocked its return date to mid-November.

However, CalMac has now said the ship's stern tube bearings and eight steel frames need repaired or replaced.

It said the ship's return date could not be confirmed yet, as there was uncertainty around the availability to dock and the extent of the work required.

The ferry operator warned that the MV Caledonian Isles could remain out of service until the end of the winter timetable in late March.

CalMac will consult with island communities later this week on a revised vessel deployment plan for winter.

CalMac’s interim chief executive Duncan Mackison said the planned work was progressing well, but the the latest issues "eliminated any chance of a return to service in the short-term".

He said: “We are in no doubt about the current challenges facing the network and the people who rely on it. We anticipated a challenging winter, and that is exactly what we’re seeing play out.

"Any decisions we take around the service off the back of this news will cause disruption in places, and we will now consult with communities to get their valuable input into that service plan.

“Our recent efforts to add resilience to the service, such as through trialling third-party vessels and by bringing forward the drydock work for MV Caledonian Isles, will continue. We will leave no stone unturned as we try to meet the needs of the island communities we serve.”

CalMac now faces a winter season without two of the 10 major vessels it normally relies on to maintain services.

The MV Hebridean Isles is due to be withdrawn from service later this month as it needs recertification and repair work is not economical.

The long-delayed Glen Sannox was due to be handed over last month, but some issues that arose during acceptance trials resulted in another delay.

Once delivered, CalMac will carry out crew familiarisation trials and the ship will not carry passengers until January at the earliest. Other vessels will also be out of service for scheduled winter maintenance.

The last time CalMac received a new large ship from ferries procurement company CMAL was in 2015, and many of its ships are now well beyond their expected service life.

Last week CalMac looked into chartering MV Ben-My-Chree from the Isle of Man Steam Packet Company, but berthing trials on the Arran route were unsuccessful.

The ship managed to berth at both Troon and Brodick but safety margins at Brodick were too tight to proceed with the charter plan.

Scottish Conservative MSP Jamie Greene said the latest MV Caledonian Isles delay was "yet another devastating blow for the residents of Arran and CalMac ferry users".

“The SNP’s incompetence has left betrayed islanders with an ever-ageing vessel which is undergoing yet more lengthy repairs, whilst the new Glen Sannox is still nowhere to be seen," he said.

“The continued absence of the Caledonian Isles will now impact the entire ferry network and, with the MV Hebridean Isles on its way to the scrap heap, there is simply no spare capacity in the network."

CalMac has a winter deployment plan in place through until Friday 15 November and the new plan will take effect from Saturday 16 November.

It will be published by Wednesday 13 November.