Union leaders are to demonstrate outside the Scottish Parliament over the future of an islands ferry service.

Grahame Smith, Scottish Trades Union Congress (STUC) general secretary, is joining the campaign called "Keep CalMac Public" demonstrators outside Holyrood which urges ministers to back the ferry firm.

He said: "The Scottish Government’s looming decision on the award of the Clyde and Hebrides ferry contract continues to be the source of great trepidation for ferry workers and users alike.

"This decision could spell the effective demise of CalMac, a great Scottish institution, and leave lifeline ferry services and the future of fragile remote communities in the hands of Serco."

He added: "I have written today to the First Minister to reiterate the STUC’s longstanding concerns over the requirement to tender and the consequences of CalMac losing out to Serco.

"Our concerns extend beyond the level and quality of employment and provision of effective lifeline services to include the ongoing viability of CalMac and the absence of an operator of last resort."

Unions including the RMT, Nautilus, Unite and TSSA will be at the demonstration.

Mr Smith added: "The Scottish Government’s competitive tender for the Clyde and Hebrides ferry services is unnecessary, expensive and hugely destabilising.

"It is crucial that CalMac is now entrusted with continuing to deliver excellent services and that the requirement to tender is urgently revisited."

It comes amid concerns over the cancellation of services on the Mallaig-Armadale service.

Dozens recently attended a public meeting in Sleat, Skye, organised by the local transport forum.

There was a huge outcry from users over the unreliability of three vessels drafted in to replace the MV Coruisk.

Since the Coruisk was deployed elsewhere, CalMac has introduced a revised timetable for its three replacement boats, two of which, locals say, cannot operate at low tide.