Campaigners fighting expansion at Heathrow have welcomed support from business leaders who have come out publicly against a third runway.

A string of top executives signed a letter to a national newspaper on Monday, stating it was wrong to assume everyone in the business community supported the expansion plans.

The 12 business figures, including the chief executives of Sainsbury’s, Carphone Warehouse and United Business Media, said “the business case for a third runway simply does not stack up”.

John Stewart, chairman of anti-expansion campaign group Hacan, said: “Gordon Brown is looking more and more isolated over his support for a third runway.

Business support for it is crumbling. This opposition from key business leaders must make it even less likely that it will ever be built.”

Russell Chambers, an adviser at Credit Suisse and one of the signatories, told the Times newspaper: “Many people in business have misgivings about the decision on the third runway, both in terms of the rationale put forward and the environmental impact.

“It’s possible to be pro-transport, pro-aviation and yet, at the same time, pro-responsible citizenship.”

The Confederation of British Industry and the London Chamber of Commerce have been strong supporters of a third runway, but the letter revealed this week it was not a view shared by all their members.

Six trade unions also came out against a third runway last year.

John Sauven, executive director of Greenpeace, said: “Everybody knows that a third runway at Heathrow will be a disaster for the climate. Now, business leaders are telling Brown that it won’t be much good for the economy either.

“The truth is that a third runway will cost billions, increase emissions causing climate change and blight the lives of millions of Londoners. It’s time Brown woke up to the fact that absolutely nobody, apart from him and the airline bosses, think this runway is a good idea.”