A LEADING opponent to Heathrow Airport expansion has warned against plans for two more runways that could potentially double the amount of flights to nearly a million a year.

Proposals to expand the south east's aviation capacity are to be submitted this summer - and there are increasing rumours Heathrow is preparing to lodge plans to upsize to four runways and increase the number of flights to 860,000 a year.

Opponents led by the 2M alliance of local authorities say the expansion would force large swathes of unused airspace to be opened up in and around London and create even greater noise on existing approaches, including over Hammersmith and Fulham.

Campaign group HACAN insist any expansion would be better served at airports including Gatwick and Stansted, which lie in far less built-up areas.

Chairman John Stewart said: "We can see the need for expanding air capacity in the south east - but not at Heathrow."

Aviation experts insist increasing flights to London is vital for the economy and say maintaining a hub airport like LHR is needed to prevent the capital falling behind rivals like Schiphol in Amsterdam and Main in Frankfurt.

Those airports, which have six and four strips respectively, are able to capitalise on lucrative transfer passengers, as well as increasing routes to emerging countries like China and Brazil.

But Mr Stewart believes London would remain competitive without expansion and says there is scope to send many flights, especially on the short-haul leisure sector, to the city's other airports.

He said: "More people come to Heathrow as a final destination than anywhere in the world - transfers are much more important to airports like Schiphol and Frankfurt. We think Heathrow could be better used with much more of a focus on long-haul and business flights. There are a lot of short flights which could go to other airports."

Mr Stewart personally believes any expansion of other airports should be done slowly and expressed concerns at the environmental consequences of a four-runway LHR.

It is said modern aircraft cause less pollution and would offset the effects of more flights. But with Heathrow already exceeding EU pollution limits, Mr Stewart has doubts and said it is a 'huge leap of faith' to say emissions could get within guidelines at a bigger airport.

With suggestions an expanded Heathrow would have its four runways further west, aircraft would come in over London higher, as well as using a steeper glideslope, but Mr Stewart said the difference in noise would be negligible.

He said: "It wouldn't be nearly as much as has been claimed - planes would only be a few hundred feet higher."

Mr Stewart's personal view is that expansion in the south east should be accomplished slowly. "It is very dangerous to predict demand 40 years ahead and it would be sensible to build one runway at a time," he added.