Chronic congestion at Heathrow Airport is driving international airlines away from the UK, according to a new survey.
More than half of scheduled airlines have plans to base flights in other countries because of the crucial London facility's lack of capacity, the poll showed.
And 86% of airlines said they would put on extra flights if more arrival and landing slots were available at Heathrow, according to the Board of Airline Representatives in the UK (Bar UK) survey.
The survey results by the industry body are being released today at a transport conference in London by BAA chief executive Colin Matthews, the Heathrow operator.
He is one of the airline and industry chiefs anxious for the Government to reverse its policy and give the go-ahead for expansion at Heathrow.
In the speech at the conference in London, Mr Matthews is expected to say: "These figures show that it is a mistake to believe that flights displaced from Heathrow will automatically fly to Stansted , Gatwick or Birmingham instead.
"The message I hear from airlines is clear: If there's no room at Heathrow then flights will move out of the UK altogether."
He went on: "Instead of Britain taking the lead in forging new links with growing economies like China, we are handing economic growth to our competitors by turning away airlines who want to bring jobs, growth and trade to the UK."
Bar UK boss Mike Carrivick, who represents 84 scheduled airlines, said the airport issue is crucial to Britain's economic vibrancy.
Mr Carrivick said: "UK business leaders should be very concerned about the restrictions on reaching new markets at such a critical time in the UK recovery effort.
"The survey's results are a chilling reminder that the Government must act decisively, and soon, in the national interest. Restricting capacity at key airports to the same level as the last decade is actively encouraging airlines and trade to go elsewhere."