SCOTLAND’s state ferry operator is challenging its owner over a £345 million contract awarded to a commercial rival.

CalMac Ferries last month failed to convince ministers to let it take over public service sea routes from the mainland to Orkney and Shetland.

The government-owned firm lost out to what it claims was a more expensive bid from private company Serco.

Now CalMac has started formally quizzing quango Transport Scotland over why it lost out to Serco. Its move means the contract, announced last month, is now in what is called “extended standstill”.

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A spokesperson for David MacBrayne Ltd, CalMac’s state-owned parent company, said: “Having won the tender for the Northern Isles ferry services on price, we are in dialogue with Transport Scotland and analysing the detailed information we requested from them about their scoring process.

“As we are still in what is now an extended standstill period, we cannot comment further.”

Islands minister Paul Wheelhouse announced Serco was the preferred bidder for the contract with news of a three-year fares freeze for island passengers and 20 per cent discounts for cabins on long routes from Aberdeen to the islands.

The franchise, called Northlink, also includes shorter hops from Scrabster in Caithness to Stromness in Orkney. The route has one of Scotland’s few non-subsidised rivals, from near John O’Groats to St Margaret’s Hope.

Serco Group Chief Executive Rupert Soames welcomed the announcement, saying: “We are very proud of our track record over the past seven years, during which time we have improved almost every aspect of the lifeline service for the communities and businesses of the Northern Isles.”

Serco ferries have not faced the same problems CalMac has dealt with in recent years.

Decades of under-investment and climate change have left the state operator with ships and ports that are often unable to offer or complete services.

Most recently, there was disruption on CalMac’s flagship route from Ayrshire to Arran earlier this month.

There was always expected to be a “standstill” period before the Northlink contract, which runs for eight years, was signed. But it was supposed to be only 10 days.

Unions and the Labour Party had lobbied heavily for public-sector CalMac to get the contract. This would have brought all of Scotland’s subsidised ferries under one state operator.

After the announcement of the preferred bidder was made, Mr Wheelhouse faced questions in Holyrood about the decision.

Scottish Greens’ Highlands and Islands MSP John Finnie quizzed him on why and how Serco was chosen.

Mr Wheelhouse responded: “Serco Ltd was awarded the status of preferred bidder on the basis of an assessment ratio of 65% price and 35% quality, as was set out in the tender documents and made clear to all bidders when the invitation to tender was issued.

“Serco was assessed as providing the most economically advantageous tender under the terms of the competition, with a tender that was evaluated under the tender criteria to provide high-quality ferry services and value for money for the taxpayer.”

CalMac told The Herald its bid was cheaper than Serco’s. This suggests Serco’s quality of service must have been judged much better than CalMac’s since price is scored twice as highly as quality.

A Transport Scotland spokesperson said: “Until the new contract for the Northern Isles ferry services is awarded this is a live procurement [and] there is a limit on what can be said at this time. However, more detailed information will be provided in due course and when it is more appropriate to do so.

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“We continue to engage with the European Commission regarding the ongoing complaint from Pentland Ferries following receipt of further approaches from the Commission.

“This will not have an impact on the Scottish Government commitment, from January 2020, to introduce a 20% discount on cabin fares on the Aberdeen-Kirkwall-Lerwick routes, as well as a three-year fares freeze for passengers, non-commercial vehicles and cabins on these routes.”

Mr Finnie challenged Mr Wheelhouse on the decision. He said: “Last year, the Cabinet Secretary for Finance, Economy and Fair Work signed a commitment to application of the fair work principles across the Scottish Government and associated bodies. RMT is in the process of taking strike action against Serco, as the operator of the Caledonian sleeper train, for reneging on pledges to address serious concerns about staff safety.

“Can the minister honestly tell Parliament that Serco is living up to the fair work principles? If not, perhaps he can explain why the fair work convention was considered to be suitable for civil servants but not for people who work in the transport sector under Serco?”