An appeal by airport operator BAA against a decision by competition chiefs to make it sell three of its airports is due to begin in London.
The Competition Commission has ruled that Spanish-owned BAA must sell Gatwick and Stansted airports and one of either Edinburgh or Glasgow airports.
BAA, which is selling Gatwick anyway, has appealed to the Competition Appeal Tribunal in a case expected to last three days.
BAA is claiming that the Commission findings requiring the selling of the airports is unlawful on grounds of "apparent bias" and "proportionality".
The bias refers to BAA's claim that a member of the Commission tribunal panel had links with an organisation interested in acquiring the airports that BAA is required to sell.
On proportionality, BAA says the Commission failed to take into account, or carry out an assessment of, material considerations of selling the airports, particularly in the context of the current financial and economic environment.
In its report, the Commission concluded that the common ownership of south-east England airports by BAA - which also runs Heathrow - adversely affected competition.
The Tribunal decision following the end of the appeal hearing is expected to take at least two months.
