The skies over Southampton could be full of aircraft if latest predictions over passengers using the city's airport prove correct.

Experts at Whitehall have warned passenger figures could rise to 7.1 million a year at Southampton International Airport if plans for expansion at Gatwick and Heathrow fail. The airport currently handles 800,000 travellers.

Government planners are to be told the move to drastically increase that number would have a "catastrophic" effect on the local road network.

The view that the airport might be capable of handling up to six million more passengers a year came from a Department for Transport consultation document on the future of air transport in the south-east.

The document warned that, if proposed extra runways at Heathrow and elsewhere were not built, bottled-up demand for flights from London airports could result in millions of people flying from Southampton instead - leading to 7.1 million passengers a year at Southampton by the year 2030.

But members of Southampton Airport Consultative Committee have drummed out a "hands off our airport" message.

They backed a call from Eastleigh council's Conservative group leader Councillor Godfrey Olson to tell government planners they were wrong about the Eastleigh airstrip which is currently handling around 800,000 passengers a year.

Supporting the move, Eastleigh councillor Colin Davidovitz said: "Whereas the airport might physically be able to deal with an increase in passenger traffic, numbers on this scale would have a dramatic effect on local infrastructure."

Speaking after the meeting, Cllr Davidovitz - who is chairman of the Eastleigh highways management advisory panel - said: "This is another instance where Whitehall planners are quite out of touch with the situation outside the London metropolitan area.

"A modest increase in passengers using the airport can be contained but an increase of six million passengers would have a catastrophic effect on our local road network which is years behind with maintenance work through reductions in government funding, and is already over capacity with existing traffic.

"The airport parking, passenger handling facilities and runways would all have to be extended and this could have a major effect on local settlements."

He added that the matter was shortly due to go before Eastleigh council's executive Cabinet and said he hoped the consultative committee's views would be endorsed.

Prominent anti-noise campaigner Mary Finch of Bitterne Park Residents' Association urged the consultative committee to oppose any change to the runway and any change to the flying controls agreement that restricts flights.

She said: "That would be drastic for the area, because of the proximity of housing all the way round."

But Peter Luffman, leader of Eastleigh council's Labour group, wondered whether future technical advances might make a bigger airport acceptable.

He said: "We all know planes are getting bigger. We all know engines are getting more powerful. There's no evidence to prove we're incapable of taking seven million.

"We should be asking questions about how we can absorb that figure."

Tim Hawkins, BAA strategic planning manager, said the company wanted the required extra capacity to be provided at larger airports.

He said: "Southampton is not in a position to help with this challenge. Its capacity is such that it can only make a very, very small contribution."

When the Department for Transport unveiled its blueprint for airport growth it ruled out a second runway for Southampton but said the government still considered it to be a vital component in the UK's airport industry.