The latest round of a battle over the sale of Stansted Airport has begun at the Court of Appeal.
Three judges in London are being asked to rule in a challenge brought by airport operator BAA.
In 2009 the Competition Commission (CC) ruled that BAA must sell Stansted in Essex and two of its other UK airports.
BAA has mounted a series of legal challenges against the decision, which have so far been unsuccessful.
The latest blow to Spanish-owned BAA came earlier this year when it lost an appeal before the Competition Appeal Tribunal.
The latest action is before Lord Justice Mummery, Lord Justice Rimer and Lord Justice Sullivan.
Since the CC decision, BAA has sold Gatwick Airport in West Sussex and faced with having to dispose of either Edinburgh Airport or Glasgow Airport, it has opted to sell Edinburgh.