Some 70 British business leaders and groups representing hundreds of others have written an open letter to government demanding the debate about building a third runway at London's Heathrow airport be re-opened.

The letter, published in the Sunday Telegraph, is signed by large corporations such as Microsoft and Telefonica O2, and puts further pressure on the government to re-think its aviation policy.

The letter was also signed by Simon Walker, director-general of the Institute of Directors, and John Longworth, director general of the British Chambers of Commerce.

Heathrow is operating at almost full capacity after the coalition government blocked development of a third runway when it came to power in 2010, as further expansion of the west London site would mean a huge increase in the number of planes flying directly over the capital.

Heathrow's operator, Ferrovial-owned BAA, last month said Heathrow was falling behind rival European airports in the battle for lucrative routes to China because of the constraints on growth at Britain's largest airport.

Earlier this year the business group London First called on the government, which recently announced plans to hold a formal consultation on proposals for a Thames estuary hub, criticised the government for ruling out a third runway at Heathrow for political reasons.

(Reporting by Rhys Jones; Editing by David Holmes)