BAA has lost its latest appeal against a Competition Commission decision forcing it to sell Stansted Airport.
The ruling is the latest in a long-running dispute over the supply of airport capacity in the south of England, with BAA already forced to sell Gatwick Airport.
The Competition Commission first ruled over three years ago that BAA must sell the properties.
BAA must also relinquish either Glasgow or Edinburgh airports in Scotland, with Edinburgh the more likely to go.
Spanish-owned BAA operates London Heathrow, Southampton and Aberdeen, as well as Glasgow, Edinburgh and Stansted.
BAA had argued Stansted served a different market to its other properties, reducing the potential for it to abuse its monopolistic position.
This view was rejected by the Competition Commission.