Scottish business leaders have called on Scottish MPs to back the expansion of Heathrow Airport in a crunch vote at Westminster today.

In an open letter, the heads of a number of Scottish airports, companies and trade bodies said a new runway at the London airport was of “critical” importance to many Scottish companies.

The controversial additional runway – which is backed by the Conservative Government but opposed by many of Theresa May’s own MPs – would not just be a piece of tarmac, the letter claims.

“It is a away of connecting people to travel and trade across the UK and the rest of the world,” it states. “Although our immediate priority should always be to grow our own route network, where a direct flight from Scotland isn’t immediately available, it is critical that we have direct and frequent access to Heathrow to fill these gaps.”

Signatories to the letter include the heads of Aberdeen Airport, Glasgow Airport, and Highlands and Islands Airports. Liz Cameron, director of the Scottish Chambers of Commerce, Stewart Patrick of Glasgow Chamber of Commerce and Mark Bevan, of the Scottish Council for Development and Industry have also signed, as has Gary Smith, secretary of the GMB Scotland.

The letter says Heathrow expansion will benefit exporters, bring new tourists to Scotland from around the world and improve logistics f or construction businesses and heavy industry.

“For our people, the runway will deliver thousands of new and skilled job opportunities. For our entire nation, the benefits of this vital piece of infrastructure are undeniable.”

“A new runway at Heathrow will mean enormous opportunities for growth, for people and businesses in every corner of Scotland,” it concludes.

The letter came as it was reported SNP MPs may reverse their position and oppose the third runway for the airport.

While previously supportive, a source told the BBC that the party’s MPs had become concerned over a lack of detail about how the new runway’s benefits for Scotland would be delivered.

The source said that, amid an ongoing row over devolution the subsequent loss of good will towards the UK Government may see the SNP abstain or even vote against the expansion