Ryanair is planning a major reduction in services from Prestwick Airport this winter, The Herald has learned.

Its seating capacity is expected to be cut by nearly a third and its number of routes from the Ayrshire hub reduced from 24 to 16.

The Dublin-based budget airline is facing increased pressure from a downturn in aviation and a rise in government passenger duty, but has so far largely maintained its destination network from Prestwick during this summer's schedule. However, its agreement to base planes at Edinburgh Airport is thought to have had a dramatic impact on passenger numbers at Prestwick, which have been compounded by the recession.

Both the airline and airport said talks over the winter schedule, which is due to begin in October, were ongoing and flights could yet be added.

However, scheduling information used within the industry, based on information supplied by airlines, shows a 30% reduction in Ryanair's seating capacity at Prestwick this December compared to a year earlier, while the network of destinations served has been reduced by eight.

Ryanair has already axed services to Bournemouth and Krakow. Among the routes due to go in October are Budapest, Milan, Rome, Stockholm and Marseille.

While most routes are relatively recent additions and have been struggling amid the aviation downturn, the list of axed destinations includes Frankfurt Hahn, a service which started in 2000 and attracted 100,000 passengers a year at its height in 2002.

Mark Rodwell, Prestwick Airport's chief executive, conceded that trading conditions were difficult but insisted it was "not all doom and gloom" at the airport.

"We are in continuing discussions with Ryanair. The flights are on sale at the moment are not the only ones we expected to be included in the winter schedule," he said.

"We currently have a 20% reduction in scheduled traffic, which is pretty much what has been expected. But we'll only finalise that about a week before the season starts."

Prestwick, whose passenger growth over the past decade has been almost solely predicated on Ryanair's agreement to base its Scottish operations there, is also heavily reliant on freight traffic and has been hard hit by the loss of Atlas Polar business last August, which contributed to freight tonnage dropping by around a half.

However, Mr Rodwell said a restructuring exercise earlier in the year, when 73 jobs were axed, mostly through compulsory redundancies, had been successful in ensuring the airport could cope in the recession.

"I am not expecting any more redundancies," he added.

Passenger numbers dropped by just over a quarter in May, according to the airport's published figures, bringing the annual total to 2.2million.

Falling revenue at Prestwick also contributed to its owner, Infratil, posting a £7.1m loss this year for its three European airports.

By contrast, Edinburgh Airport recently posted its third successive month of passenger growth.

Brian Donohoe, MP for Central Ayrshire, said concern over the drop in passenger numbers had led him to seek assurances from both Ryanair and Prestwick about the airline's commitment to the airport.

But he said he was convinced Ryanair was not planning to pull out and would see long-term growth.

He said: "I have no doubt that, in the next 18 months, business will increase at Prestwick, and Ryanair is committed to keeping five planes based at the airport."

A spokesman for Ryanair refused to discuss what he called "speculation and rumour".

He added: "We haven't announced our winter schedule yet and haven't finalised routes or capacity with any of our airports yet."