Almost £100m has been spent over the past decade on repairs for eight of the largest publicly owned ferries in Scotland.

The figure has been described as “eye-watering” by Sue Webber, transport spokesperson for the Scottish Conservatives, who obtained details of the repair bill from ferry operator CalMac.

The disclosure will add to the controversy surrounding Scotland’s “ferry fiasco”, which has led to major disruption of transport links between islands and the mainland. At the same time, construction of replacement vessels has suffered huge delays while costs have quadrupled.

The MV Caledonian Isles – which sails between Ardrossan and Brodick, on the Isle of Arran – cost the most to repair, it was revealed on Saturday. More than £22m was spent on work on the ship, including £7m on repairs that kept the ferry out of service for most of last year. It is still not due to return to service until March.

Repairs to the MV Isle of Lewis cost just over £15.2m, while £14.6m was spent on the MV Lord of the Isles and £14.4m on the MV Isle of Mull. The other vessels on the repair list were the MV Argyle, MV Finlaggan, MV Loch Dunvegan and MV Loch Seaforth.

Webber accused the Scottish government of running the ferry network “into the ground”, and attacked ministers for betraying islanders “at every turn” and leaving them “relying on out-of-date vessels”.

“Targets have been missed time and time again and it is high time that ministers were held to account for this appalling and unforgivable ferry fiasco,” she said.

CalMac’s fleet is currently undergoing a revamp, with six new vessels – including the late and over-budget MV Glen Sannox and MV Glen Rosa – due to enter service in the coming years to replace the ageing ferries already in use. Along with seven new small vessels currently out to tender, a third of the fleet is likely to soon be replaced.

“The replacement programme will provide more reliability of service, which is what islanders need and deserve,” said a spokesperson for Transport Scotland. “In the meantime, it is essential from a health, safety and reliability basis that maintenance and repairs are carried out on vessels where and when needed.”

A spokesperson for government-owned operator CalMac said the repair bill had been essential to maintaining a reliable ferry service. “A third of our fleet is now operating beyond their life expectancy,” they said. “We have experienced very significant cost increases over the last few years due to market conditions, alongside the increased costs due to the repair and maintenance requirements of an ageing fleet.”