Airport operator BAA will still have to sell two of its UK airports following a provisional ruling by the Competition Commission (CC).
The commission had ruled in 2009 that BAA would have to sell Gatwick and Stansted airports as well as either Edinburgh or Glasgow airport.
Since then there have been legal challenges by BAA to the ruling, which ended with the CC findings being upheld.
BAA has already sold Gatwick and on Wednesday the CC provisionally concluded that the sale of the other airports should go ahead.
The CC said it remained convinced the original sale decision was "the right one for passengers and airlines", adding that Stansted should be sold first, with a "small overlap" between that sale and the sale of one of the Scottish airports.
BAA said: "We will carefully consider the CC's provisional decision before making any decisions or further statements. We believe that there has been a material change in circumstances since the commission's report was published in March 2009."
Stop Stansted Expansion campaign director Carol Barbone welcomed the CC provisional decision: "BAA has spent over two years appealing the commission's original verdict and all it has succeeded in doing is prolong the agony for employees and local residents alike," she said.
"BAA should now end its pointless defiance of the commission and allow Stansted to have a new owner as soon as possible. This, at least, will provide some chance of tackling the blight which BAA has caused over the last decade."
Gatwick was bought by US-based investment fund Global Infrastructure Partners which already owned London City Airport.
Gatwick chief executive Stewart Wingate said: "It is welcome news that the CC remains convinced that competition in the airport market is a good thing and that a further break-up of BAA should press ahead."