A THIRD runway at Heathrow would "stifle competition" and leave Scotland "feeding a steroid-enhanced" hub at the expense of its own growth, the chairman of Edinburgh Airport has warned.

Sir John Elvidge, said the case for expanding Heathrow was based on an "old-fashioned assumption that we in Scotland are to be forever dependent on a giant monopoly airport in the South East".

Writing in the Herald today, the Scottish Government's former permanent secretary urged David Cameron to rethink proposals for adding a third runway at Heathrow amid reports that the SNP could - as the third largest party at Westminster - could hold be key to driving the development forward in the face of opposition from other parties and some Conservative MPs.

Sir John said Scottish passengers had benefitted from increased competition after the break up of BAA, which transformed Glasgow and Edinburgh airports into rivals where previously they had been members of the same group.

More recently, Glasgow and Aberdeen airports were sold off by Heathrow Airport Holdings.

Sir John said: "The story of Scotland's recent success in growing our share of international air travel is one of stepping out of an ownership structure for airports in which everything was overshadowed by a focus on Heathrow.

"We now have to be aware of the risks that building a new runway at Heathrow would bring. The view of the Airports Commission that Heathrow is the answer to the UK’s long-running capacity question threatens to stifle competition by creating a new and expensive monopoly.

"Heathrow’s case for the nations and regions of the UK is built on an old-fashioned assumption that we in Scotland are to be forever dependent on a giant monopoly airport in the South East for our long-term economic success and prosperity."

Edinburgh Airport is owned by Global Infrastructure Partners (GIP), the same investment fund which owns Gatwick Airport - Heathrow's rival in the expansion battle.

A long-awaited report by the Airports Commission, published in July, concluded that a third runway at Heathrow was the "clear and unanimous" winner over Gatwick's bid for a second runway.

The Heathrow option has also been widely backed by Scottish business groups, including the Scottish Chambers of Commerce and the Scottish Council for Development and Industry (SCDI).

However, the report warned that Scotland could end up with even fewer connections to an expanded Heathrow than it has now unless the Government reformed the way it uses public subsidies to support domestic routes

The number of services between Scotland and Heathrow has tumbled from 50 to 35 in the last decade. Inverness has had no daily connections with the hub since 1997 while flights to Heathrow from Glasgow and Edinburgh have been cut by a third in the last 20 years.

Heathrow bosses have promised their plans will deliver lower fares, better timed and more frequent flights between Scotland and Heathrow, and the return of direct flights with Inverness.

They also say it would make it cheaper for Scottish manufacturers to export their goods across the globe as a third runway would double freight capacity at Heathrow.

The London airport's chief executive, John Holland-Kaye, said: “An expanded Heathrow will deliver jobs and growth for Scotland – creating over 16,000 new skilled jobs and delivering up to £14 billion in economic growth.

"With more capacity at the UK’s only hub, it’ll also be cheaper for Scottish exports to get to market with up to 40 new long haul links. Scottish passengers will see new connections to cities like Inverness, increased competition on existing routes and lower fares as low-cost carriers like easyJet boost links between Scotland and an expanded Heathrow.”