SCOTTISH Government ministers are “testing the market” again to try to find a buyer for Prestwick Airport.

The Times reported that the move was noted in newly filed annual accounts for the Ayrshire hub, which confirmed the amount it owes to the public purse has increased to £55.5 million.

Prestwick received £43.4m of loans to help stabilise it in the years following its nationalisation in 2013, when it was moved into state ownership for a token £1.

Although Prestwick has not received any fresh borrowing in recent years, the accrued interest on the loans increased by more than £3m in the most recent financial year to stand at a total of £12.1m. None of the interest or original loan sum has yet been repaid.

Accounts for the 12 months to March this year showed a near doubling of pre-tax profit to almost £1.5m, even though revenue dipped by 7% to £54.1m.

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Chairman Willie Mackie said Prestwick had now been in profit for five consecutive years, adding: “Market conditions remained challenging, however we have seen further tangible evidence that our strategic focus across the business is delivering positive trading results.

“The directors and the executive team remain fully committed to maximising the potential of the airport and to delivering the maximum return to our shareholder.”

Fuel sales, which largely come from military customers, made up the bulk of revenue at £34.1m, compared to £40.8min the previous financial year.

The Royal Air Force, as well as the Canadian and US air forces, were among regular customers while a Nato exercise had also been supported during the year.

Cargo and fixed base operations both recorded lower revenue in the period while property, aerodrome and passenger activity went up.

The airport said there were 523,000 passengers across the year, compared to 459k the previous year, with Ryanair the only airline running flights. The Irish carrier also has a repair and maintenance base at Prestwick.

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Fuel volumes at the airport increased, from 44m litres to 46m litres, but pricing was weaker.

A number of attempts have been made to drum up interest in Prestwick, with two anonymous preferred bidders having been selected in the past although neither completed a deal.

Earlier this year Forsyth Black resigned as Prestwick’s chairman to work on a potential bid with Onex Corporation, a Canadian investment firm.

The Prestwick accounts said: “It has been a long-term aim for the Scottish Government to return the airport to the private sector and the board, the Scottish Government and their advisers are currently engaged in a process in testing the market.

“The board remains committed to ensuring that any potential transaction aligns with the best interest of the airport.”

Airport bosses said new partnerships would help to boost cargo traffic. One with Royal Mail was announced in June, aiming to attract e-commerce goods, while a second deal, with an as yet unnamed airport in the US, is looking to create a transatlantic corridor for aerospace goods.

Prestwick chief executive Ian Forgie said: “Our diverse business streams are proving to be robust and adaptable allowing us to capitalise on growth opportunities even in a challenging market environment.”

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A Scottish Government spokesperson said: “In June this year the Scottish Government updated the Parliament on the status of Glasgow Prestwick airport and confirmed that expressions of interest had been received.

“It would not be appropriate to share further details, including the number or identity of any other organisations behind an expression of interest, at this time.

“The Scottish Parliament will be updated when appropriate.”