THE number of passengers using Plymouth Airport could rise from about 80,000 a year in 2006 to 580,000 by 2021, according to plans for the north of the city.

Environmental activists hit back yesterday, saying that calls to expand the airport fly in the face of Government policy.

But one pro-airport campaigner warned that if the airport failed, Plymouth would be "up the creek".

The fate of the airport is a key issue in the council's draft area action plan for Derriford and Seaton, which goes out to public consultation next month.

It is run by Plymouth City Airport Limited, part of Sutton Harbour Holdings, which operates commercial air services through Air South West.

Last year Sutton Harbour Holdings invoked a clause in its 150-year lease that allows it to sell off the shorter of the airport's two runways, and in November Plymouth City Airport Limited applied for outline planning permission to develop housing, office space and a care home on the surplus land. It also applied for detailed planning permission for a airport improvements.

A 2006 study found that the airport could handle 530,000 passengers a year. The next generation of aircraft could push usage to 580,000, but the main runway would need to be extended. The South West Regional Development Agency, has already said it will not fund an expansion in passenger numbers, though it would contribute towards "greening" airports.

Roger Creagh-Osborne, Plymouth Green Party spokesman, said that any attempt to expand the airport to take half a million passengers a year was "just mad" and took no account of last year's Climate Change Act. "They are living in the 1990s and they need to look at the commitments the Government has made on reducing carbon emissions," he said.

"Newquay claims its expansion will bring economic benefits, but their airport is a massive drain on the county, and the same would be true of Plymouth."

Labour group leader Tudor Evans said: "The issue is continuing to make sure that we have a good, strong business link for journeys to the capital. The council needs to address that, and time is running out.

"I don't know whether Plymouth would be well served by trying to compete with Exeter. Taxpayers here have already spent a lot of money to develop Exeter as an international airport.

"There would be two airports hellbent on oblivion rather than two airports serving different markets."

John Dixon, the council's spatial planning co-ordinator, said: "It's part of our core strategy to increase passenger numbers, but we are looking at ways of reducing the impact."

Airport campaigner Sid Anning has been arguing for an expansion of the airport.

"Because of width restrictions we are not talking about Jumbo jets landing in Plymouth," Mr Anning said. "All we want is to see the runway lengthened to take 75-seater Dash 400s.

"If Air South West offers new routes into Europe we could take business from Exeter and Newquay.

"The worst news is that from next month Flybe will be operating on the Gatwick route, which is bread and butter for Air South West. If the airport closes, Plymouth will be up the creek."

Alison Seabeck, the MP for the north of the city, said: "The council has to come off the fence and acknowledge that our city does need an airport.

"We're working hard to ensure that Plymouth does not lose out to Newquay, but we have to look at improving the environment and the buildings. We have to make it a much more appealing airport than Exeter."

Ted Fry, the city council deputy leader, said he believed that Plymouth and Newquay airports could co-exit.

"One depends on the other, and if either closes the other will have problems," Mr Fry said.

Nigel Godefroy, chief executive of the Sutton Harbour Group, said: "We are fully behind the need to support the growth of the city airport but any an extension will depend on future demand and sources of funding."