The capital benefited from the fifth consecutive month of growth, with the success of Edinburgh festivals last month helping to attract thousands of international visitors and pushing a 4.8% increase in passenger numbers.

Heathrow, the UK’s biggest airport, also enjoyed its busiest month ever after recording marginal growth in August, with an increase in leisure travel making up for a steep downturn in business flights, owner BAA said.

However, traffic at the remainder of the seven airports under BAA’s ownership decreased, leading to an overall decline in passenger numbers of 3.1% compared to last year, indicating that the slowdown in aviation is yet to abate.

By far the worst performer was Glasgow International Airport, which saw 13.4% fewer passengers in August compared to a year previously. In the space of two years, the airport has lost nearly 1.4 million passengers as the recession has taken a particularly big bite out of its traditional bucket and spades charter holiday market.

Aberdeen suffered the second biggest loss, with 9.8% fewer passengers last month than August 2008.

However, aviation analysts said there were tentative signs that the industry was stabilising as BAA’s traffic figures showed a slight increase in the number of scheduled flights to European destinations.

A spokeswoman for BAA Scotland said Edinburgh’s growth could be largely ascribed to budget carrier Ryanair’s decision to operate a base there. She said: “With five consecutive months of rising passenger numbers, Edinburgh is one of the few UK airports currently enjoying a period of growth, largely as a result of Ryanair’s substantial growth and the success of this year’s Edinburgh Festival.

“International traffic was particularly strong as the city welcomed tens of thousands of overseas visitors for this year’s Festival.”

Glasgow Airport faces further pressure over the winter months from Ryanair’s decision to concentrate on sunshine destinations from nearby Prestwick Airport, which have traditionally been served by its bigger rival, putting it into more direct competition with easyJet and Flyglobespan.

Laurie Price, director of aviation strategy at consultancy Mott MacDonald, said: “Growth has definitely ­shifted from west to east over the last 10 years, which has been helped by the establishment of the Scottish Parliament. When airlines are looking to set up a route to one point in Scotland, they have tended to go to Edinburgh.”

Mr Price predicted that the competition between Prestwick and Glasgow airports would lead airlines to cutting destinations. “If you look at the actual exchange rate with the euro, it’s almost one to one. People are worried about their jobs so it’s not surprising that traffic to Spain is down by 10% to 15% in certain markets,” he said.

“Competition will be good for consumers in the short term until someone pulls out. I think Glasgow will be under pressure but its economy of scale will help it to fight back more than Prestwick, which is really on the periphery of the market.”

In the past year, passenger numbers have declined by around a quarter at Prestwick, which is almost entirely reliant on Ryanair for its scheduled flights.

The Irish no-frills operator announced in July it was axing routes to Frankfurt, Krakow and Stockholm to concentrate on popular tourist destinations in the Mediterranean and Canary Islands.