A public inquiry has begun into plans to expand Stansted airport.
BAA intends to increase passenger numbers in the Essex airport from 25 million to 35 million per year and increase permissible air traffic movements from 241,000 to 264,000.
But the plans have been rejected by Uttlesford district council and a decision over the proposals has been left to the inquiry.
The first day of the inquiry was met with a colourful protest outside the building where it was being held, Endeavour House, by the Stop Stansted Expansion campaign group.
Carol Barbone, the group's campaign director, said: "If Stansted were permitted to expand to maximum use of the existing runway, the local environment would suffer, the national economy would suffer and we would have taken a giant step backwards in the battle to combat climate change."
"The inquiry will need to decide whether it is more important to start combating climate change or to provide more cheap flights to Prague," she said.
The plans have provoked the ire of environmental groups and the Liberal Democrats, who claim it is a measure of the government's tenuous commitment to lowering carbon emissions.
Alistair Carmichael, Liberal Democrat transport spokesman, said: "It is time for Gordon Brown to start practicing what he has preached on the environment.
"Rather than encouraging money to be spent on increasing airport capacity, the government should help cut down on internal flights by making sure Britain's railways are fit for the 21st century," he said.
"Allowing further expansion of airports in the south-east would be utter madness."
But BAA claim the expansion of the airport can be achieved in an environmentally sustainable way while delivering a host of economic benefits to the area. They stress the fact that the expansion is environmentally preferable to building any further runways.
"After a great deal of consultation and study by the government, aviation policy is very clear - the first priority is to make the best use of our existing single runway. We believe that we can do this with the minimum impact on the environment and maximum benefit to very many people," a BAA spokesman said.
"The fact remains that more people want to fly to more destinations, more often than ever before, and we are very confident of the case we will be presenting that says we can achieve growth in a sustainable way."