FERRY service cancellations hit their highest level in a decade last year as Scottish island communities were cut off by a barrage of weather-related problems and technical faults with vessels.

On one route - Mallaig to Lochboisdale - more sailings were scrapped than actually ran last year, while a number of others saw one in every ten scheduled services cancelled, including Oban to Colonsay and Mallaig to Eig, Muck, Rum and Canna.

Overall, passengers have benefitted from a 4.8 per cent increase during the decade in the number of scheduled sailings linking the mainland and isles - but this has been offset by a 124 per cent spike in the number of cancellations, eroding the reliability of the lifeline service.

Although the bulk of cancellations are due to weather, with CalMac previously revealing that worsening conditions off the course of Scotland was harming its reliability, there has also been a rise in breakdowns and technical faults with vessels over the last three years - although CalMac denied they were becoming more common.

The number of weather-related cancellations in the last two years also far outstripped 2009/10 and 2010/11 when Scotland endured its harshest winters in decades.

Mick Cash, General Secretary of the Rail, Maritime and Transport Workers union (RMT), said: "With an ageing fleet and weather related problems occurring almost as often in summer months in recent years as at the height of winter RMT are not surprised at the increase in scheduled sailings being cancelled.

"Governments at both Westminster and Holyrood have failed to invest adequately in public transport both on the rail network and on this lifeline ferry service."

It comes as passengers face major disruption from three days of industrial action by CalMac employees over job security, pensions and conditions.

RMT members among the workforce will refuse to work overtime today and tomorrow before staging a strike on Friday over fear of staff cuts and changes to pay and conditions when the current contract ends in October 2016.

CalMac currently predict that the majority of services will run on Wednesday and Thursday, but they expect disruption on Friday with major vessel routes serving the Western Isles, Mull, Islay, Bute, Arran, Coll and Tiree expected to be severely affected, and only supported by smaller vessels in most cases.

CalMac and Transport Scotland have made contact with bus, rail and aviation operators to see what additional services can be provided to help mitigate the impact.

Critics have raised fears that the service could be "privatised by the back door" with Serco, the current Caledonian Sleeper operator, bidding against incumbent operator CalMac Ferries Ltd to take over the Clyde and Hebrides contract for up to eight years.

The Scottish Government said the contract had to be put out to tender to comply with European rules, but Mr Cash claimed the tendering process was "taking much needed resources both in financial and managerial and engineering expertise away from the competent running of this lifeline service".

Regardless of who wins, the network infrastructure - ferries, ports, and harbours - will remain publicly-owned through Caledonian Maritime Assets Ltd (CMAL).

In 2014/15, almost 5000 of all scheduled sailings across 27 routes were cancelled, compared to fewer than 2000 five years ago.

LibDem MSP for the Highlands and Islands, Tavish Scott, said: "Islanders will be worried by the remorseless rise in cancellations. These are lifeline services and the islands need them to run. Weather is no one's fault, but the rise in technical problems needs to be solved and solved quickly. It is time for Ministers to ask hard questions about reliability of their service."

Rhoda Grant, Labour MSP for the Highlands and Islands said the figures partly reflected a more "risk averse" attitude to weather, but called for islands communities to have a greater say in the running of the service.

"We need to get a board that's more representative and disperse staff across the islands," she said.

A spokesman for CalMac said: "We increasingly aware of significant changes in prevailing weather conditions. In recent winters, our masters have witnessed an increase, not only in the severity of extreme weather events but also in their duration and frequency, all of which have impacted on our fleet's ability to operate services safely.

"Such extreme weather events also have a considerable impact on the ability of the ports and slipways we operate from to safely support the delivery of our ferry services.

"The safety of our vessels, crew, passengers and port facilities is our number one priority. Of course we fully appreciate our customers' frustration that weather changes are leading to an increase n disruptions across our network.

"But there is no quick fix to this and it will be a factor that will need to be taken into account when replacing ships and upgrading harbours in the future.

"Technical breakdowns remain infrequent, 535 last year out of 134,665 sailings, and are by their very nature unpredictable, there is no clear pattern over the past ten years that they are becoming more common."

A spokesman for Transport Scotland added: "The decision to delay or cancel a sailing is never taken lightly as CalMac fully recognises the importance of ferry services to the island and rural communities.

"Transport Scotland regularly monitors the reliability and punctuality of all lifeline ferry services in Scotland and keeps Ministers up to date on disruption to the network."