PRE-TAX losses at Scottish Government-owned Prestwick Airport have doubled amid a "challenging year" which has seen passenger traffic plunge by nearly a third.

The latest results show that while turnover has increased £600,000 year-on-year, this has been overshadowed by a £5m surge in costs associated with running the Ayrshire base.

Pre-tax losses have also gone from £4.6m in 2013/14 to £8.9m in the last financial year, though this was driven by £4.5m worth of write-downs on the company's assets to bring them into line with their value in the current market.

Without that, the trading performance showed a marginal improvement of £200,000 year-on-year. It is also improved from its last full-year of private ownership, under New Zealand firm Infratil, when the annual pre-tax loss at March 2013 stood at £9.8m.

The Scottish Government bought the airport for £1 in November 2013 to save the site from closure.

Loan funding from Scottish Ministers, meanwhile, increased from £4.5 million at the end of the last financial year to £10.8million in March 2015. This is projected to increase to up to £25m in taxpayer loans by the end of March next year.

The figures have been submitted to Companies House by TS Prestwick Holdco Ltd, the holding company created by the Scottish Government to buy shares in the airport and oversee its corporate governance.

It coincides with a 30 per cent decline in passengers over the last year, according to figures lodged with the Civil Aviation Authority.

In May 2015, passenger traffic had fallen from around 100,000 the previous May to 69,613 - roughly the same as Glasgow Airport handled every three days and Edinburgh Airport handled in two days.

Figures for June this year are not yet available.

Iain Cochrane, chief executive of TS Prestwick Holdco Ltd, said the airport's ability to attract new passenger services was hampered by air passenger duty, which the Scottish Government wants to halve and eventually scrap when control over the levy is devolved to Holyrood.

Mr Cochrane said: “Following another challenging year the airport continues to work to turn around the financial performance and there are promising signs in a number of areas, though growing the passenger business remains a challenge whilst Air Passenger Duty exists at its current level.

"The airport is a front runner in the process to become the first designated UK Spaceport and is continually looking for opportunities to maximise both income and the broad scope and opportunity offered as a strategic national asset.”

Ryanair remains the only passenger airline operating out of Prestwick Airport, but it has repeatedly cut the number of services and relocated others to its new Scottish base at Glasgow Airport.

In November 2014, aviation consultant Andrew Miller was appointed chair of the Holdco's subsidiary, Prestwick Aviation Holdings Ltd, to help turn the business around.

He was joined in June this year by four non-executive directors - Gordon Arthur, Ken Dalton, Bob Goldfield and Jane Maclennan.

A spokesman for the Scottish Government said rescuing the airport had safeguarded more than 3000 jobs and secured an asset worth £61m a year to the Scottish economy.

He added: “These financial results are as we expected. As we made clear at the start of the acquisition process, this is a long term investment. There is no quick fix to turn Glasgow Prestwick Airport around, but there are real opportunities to improve in all areas of the business.

“Our investment is on a commercial basis and takes the form of loan funding. This attracts a market rate of interest in line with state aid rules. The recent Audit Scotland report confirmed that we are highly likely to generate a return on this investment."