All 60 passengers, including an infant and children, have been returned to land safely after a ferry ran aground, but a union has urged for a probe into the "major incident".

The MV Pentalina issue a Mayday call off Orkney on Saturday evening after smoke was detected in the engine room. 

Pentland Ferries had confirmed 60 passengers, including three children and an infant, were on board the vessel - which had only returned to the service this week. 

RNLI vessels were called to the scene near St Margaret's Hope at approximately 7.30pm. 

They helped evacuate the passengers and some of the crew but eight staff members remained on board to help manage the situation. 

On Sunday morning, MV Pentalina was refloated and towed to its berth.

The coastguard has since confirmed will now be surveyed to establish the extent of any damage and monitored for pollution.

Marine Accident Investigation Branch, which investigates all maritime accidents in UK waters, has been informed of the incident.

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A spokesperson said: “The MV Pentalina was refloated at approximately 5.30am today after a tow was established by a tug whose services were acquired by Pentland Ferries.

“The Pentalina was brought alongside its berth in St Margaret’s Hope a short while later. HM Coastguard’s Emergency Towing Vessel MV Ievoli Black observed the operation, alongside counter-pollution officers, and reported that there were no signs of pollution.

“The vessel will be surveyed later today to establish the extent of any damage while the harbour master will continue to monitor for pollution. MAIB (Marine Accident Investigation Branch) has also been informed.”

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The MV Pentalina returned to the route to allow the MV Alfred to service CalMac routes on the west of Scotland. 

The RMT union has called for a "thorough investigation" into the "major incident". 

A statement from Pentland Ferries on Saturday evening said smoke was detected in the engine room before the vessel grounded, adding: “The safety of our passengers is, of course, our first priority.”

The ferry company later said: “All passengers that were onboard MV Pentalina tonight are safe and are either at home or at their accommodation.

“Our customer services team are contacting all customers that are due to travel. Further updates will follow.”

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An RMT union spokesman said: “A thorough investigation will be needed to establish how this major incident aboard the Pentland Ferries vessel occurred.”

Scotland’s transport minister Kevin Stewart tweeted on Saturday evening that he was “sorry” to hear of the incident, but that “all on board are safe and well and that emergency services are in attendance”.

Scottish Conservative MSP Jamie Halcro Johnston has also raised questions about how long islanders will face a "severed" link to the mainland after the latest breakdown. 

He said: "This is a hugely concerning incident and one which could have had catastrophic consequences. 

“Mercifully, all the passengers on board appear to have been evacuated unscathed thanks to the superb efforts of the RNLI, our emergency services and the MV Pentalina crew.

“The Pentalina was only summoned back into action this week because the MV Alfred had to be seconded from Pentland Ferries to help plug gaps in the ageing, unreliable CalMac fleet.

“While it will be important to know just how this incident came about, my immediate concern is for what this means for Orkney and how long this vital link for our islands will be severed. 

“There are a number of questions the Scottish Government needs to answer, including whether the £9m agreement between CalMac and Pentland Ferries allows for the MV Alfred to be recalled to Orkney early, or if the Alfred will stay on the west coast and Orkney will be left without a key service."

He said that the incident exposed the "pitiful lack of resilience in Scotland’s ferry network".

The MSP added: “This all stems from the SNP’s appalling record on vessel procurement – and in particular the delayed delivery of the infamous Ferguson Marine boats – which has left CalMac with decrepit ferries that are breaking down on a regular basis.

“Scotland simply doesn’t have enough working ferries to plug all the gaps left by 16 years of SNP mismanagement. Our island communities cannot continue to suffer due to their shameful neglect of lifeline services.”