MSPs have voiced concern after it emerged the Scottish Government has now loaned almost £50m to a struggling firm owned by a billionaire adviser to Nicola Sturgeon.

Ministers announced earlier this year that they had loaned £30m of public money to ferry builder Ferguson Marine, the last commercial shipyard on the Clyde.

However it has now emerged that the government also gave a £15m loan to the firm, owned by Monaco-based engineering tycoon Jim McColl, in September last year.

The information was shared with Holyrood’s finance committee but withheld from the taxpayers who ultimately supplied the funds because of “commercial confidentiality”.

At the time, Ferguson Marine was struggling to meet the deadline for filing its accounts.

It was due to lodge its annual statements for 2016 by 30 September 2017.

It failed to do so, and has still not filed them with Companies House, meaning its last full-year public financial disclosure covers the year to 31 December 2015.

Mr McColl, who sits on the First Minister’s council of economic advisers, bought Ferguson Marine in Port Glasgow after it went into administration in 2014.

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The following year Ferguson’s won a £97m Scottish Government contract to build two new ‘dual fuel’ ferries for government-owned CalMac, securing work for the 150 staff.

However the contract has not gone smoothly, with the two vessels delayed from summer and autumn of this year to summer 2019 and spring 2020, despite Mr McColl personally reassuring ministers last year that the boats would be delivered on time.

In June, Finance Secretary Derek Mackay announced a £30m loan to Fergusons to help the firm “diversity” into low-carbon marine projects and decommissioning work.

“The loan is a strategic investment in our industrial capability as both the marine engineering sector and commercial shipbuilding have vital roles to play in Scotland’s future,” he said.

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However Mr Mackay made no mention that he had already loaned Ferguson up to £15m just nine months previously, and that this had already been fully drawn down by April.

That information only emerged after the Scottish Government was asked under freedom of information law if it had given any public funds besides the declared £30m loan to Ferguson Marine or to Mr McColl’s Clyde Blowers empire, which ultimately owns the enterprise.

The government replied: “In September 2017 the Scottish Government agreed to provide a commercial loan facility of up to £15 million to Ferguson Marine Engineering Limited.

“This facility was fully drawn in the financial year 2017-18 and the expenditure will be recorded in the Scottish Government’s Consolidated Accounts for 2017-18 when they are published in September 2018.”

A government spokesman added: “Scottish shipbuilding has a long and proud history, and it is essential we continue to support the industry to thrive and help it reach its full potential.”

Tory MSP Jamie Greene said: “This is a significant sum of public money secretly provided to a private company and the SNP has conspicuously failed to announce it or explain it.

“This revelation raises many serious unanswered questions: most importantly, why was this initial £15m given to Ferguson marine and what was the money spent on?

“The SNP must urgently clarify both the process by which Ferguson Marine received £45m of taxpayers’ money and outline the loan terms and when or if taxpayers will see any return.”

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Labour MSP Colin Smyth linked the cash to a “fundamental problem” with the delayed ferry orders, adding: “The lack of action by the Scottish government means more and more taxpayers’ money is being poured in and these latest revelations show there has been a lack of transparency from government on how much.”

Ferguson Marine Engineering has blamed unforeseen complexities with the ferry order for delays, as the vessels are of a novel duel-fuel type, pushing up costs.

A spokesman said: “As we work with to resolve these claims with [CalMac owners] CMAL, the Scottish Government has provided us with two commercial loans in the amount of £15m and £30m. These loans also support the further diversification of the business and the securing of new contracts for the yard.”