European air pollution rules will block expansion of Heathrow airport for at least a decade.

BAA has conceded it will not get planning permission for a third runway until the high level of pollutants around the airport recedes.

This can be solved only with the introduction of cleaner car and aircraft engines, which are unlikely to be widely in use until 2016 or later.

"If you look at it economically, there is no doubt that the right decision is to expand Heathrow," said a BAA spokesman.

"But a number of environmental problems have to be resolved, most importantly the air-quality issue. If the government is not convinced it can be resolved, then our position is that ministers would be right to bring forward another scheme.

"And since we don't think that the Gatwick agreement should be infringed, that points to Stansted."