The UK Competition Commission ordered BAA, owner of London Heathrow and five other UK airports, to sell Stansted, the UK's second largest air cargo hub.
The company must also dispose of either Glasgow or Edinburgh airport after the commission confirmed an earlier ruling in 2009 that it must sell three of its seven UK airports within two years.
BAA, which is majority owned by Spanish infrastructure group Ferrovial, has already sold London Gatwick to U.S.-based Global Infrastructure Partners for $2.4 billion.
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BAA has mounted several legal challenges against the decision of the competition regulators arguing that circumstances had changed "significantly" since the original ruling, most notably the government's rejection of any new runways in southeast England.
But the Appeal Court backed the original ruling in October, and BAA lost its bid to appeal that decision in February.
The Competition Commission March 30 said Stansted must be sold first with a "small overlap" between its disposal and that of one of the two Scottish airports.
Stansted, 35 miles northeast of London, is a major cargo and express airport, handling 203,000 tons of freight in 2010, up 10.4 percent on the previous year.
BAA would still be a major player in the air cargo market through its ownership of London Heathrow, Europe's third largest cargo hub after Frankfurt and Paris Charles de Gaulle.
BAA handled 1.7 million tons of freight at its six UK airports and Naples, Italy, in 2010, an increase of 14.2 percent on the previous year.
BAA said it would "carefully consider" the Commission's ruling before deciding how to proceed.
-- Contact Bruce Barnard at email@example.com.