Prestwick and Marsden airports made a combined loss of £18.02m last year
Prestwick Airport owner Infratil has reported further writedowns on the value of its UK airports assets.
Infratil, a New Zealand-based infrastructure investment firm, posted a 10 per cent rise in annual revenues on Tuesday to NZ$520.2 million (£250.9 million), ahead of expectations.
However, the group said Glasgow Prestwick and Manston Airport in Kent contributed a combined after tax loss of NZ$37.4 million (£18.02 million) for the 2011 year.
Infratil said the asset value of the airports was also written down by a further NZ$26 million (£12.5 million) last year on top of a NZ$34.4 million (£16.5 million) writedown the year before.
The group appointed PwC as its advisors to sell off the UK airports in March.
Infratil confirmed in an annual report published on Tuesday the marketing process is now underway for the divestment of both airports, and offers from interested parties are being actively sought.
Passenger numbers at Prestwick for the first three months of 2012 were down a third on the same period last year.
In the 12 months to the end of March 2012, 1.22 million passengers went through Prestwick Airport, down 300,000 on the previous year.
The drop in passenger numbers was said to be largely from budget airline Ryanair cutting back its services from the airport.
Freight figures in the first three months of 2012 dropped to 2,925 tonnes from 3,300 tonnes for the same period a year earlier.
Transport group Stagecoach sold Prestwick Airport to Infratil in 2001 in a deal worth £33.4 million.