THE value of Prestwick Airport has plummeted to less than one-quarter of the level it was at two years ago as owner Infratil struggles to find a buyer for the Ayrshire site.

The New Zealand-based company yesterday put the value of Prestwick and Manston Airport in Kent at £10.5 million. They had been valued at £32m earlier this year. A valuation carried out at the end of the financial year in March 2011 said the airports were worth £44m.

Both airports were put on the market in January after their parent company said

they were under-performing. It had been hoped a sale would be completed by early next year.

Passenger numbers at Prestwick have dropped to just under 1.1 million a year – less than half the level of four years ago – as budget airline Ryanair, which provides the bulk of passenger flights, has relocated many services to Edinburgh.

The latest devaluation follows warnings in September by Ayrshire MP Brian Donohoe that the lack of investment had left Prestwick looking tired and off-putting to potential buyers.

He said the latest statement by Infratil, carried out ahead of interim financial statements next week, showed there was a need for investment. "I'd like it to be sold for a pound, frankly, seeing as they're losing money there," he said.

Mr Donohoe added: "I want someone to come in with the clear understanding that investment is needed. They need to invest £10m in the airport – and sooner rather than later. It's only when that investment happens that you will get one of the big charter airlines coming in."

Infratil's purchase of Prestwick from Stagecoach for £33.4m in 2003 was overseen by the aviation consultancy MPD Group. John Baillie, operations director at the consultancy at the time, said: "Infratil has written down the value of the asset on its balance sheet, which would appear to be a reaction to the lack of interest from the market in the airport."

Infratil said in its statement: "Infratil continues to actively seek a buyer for the airports, while considering all other options available with respect to the ongoing operations."