In a statement released on Wednesday, Ryanair said it wants Ferrovial (FER.MC)-owned BAA to revise the current price cap in place at London Stansted airport. It also said BAA had overcharged airlines for the last five years and had inflated its costs and its regulated asset base RAB.L.

"BAA Stansted's regulatory accounts show numerous examples of unexplained costs being transferred to Stansted by BAA and Heathrow which inflates Stansted's costs and understates Stansted's profits, while boosting those of the BAA Group and Heathrow," the company said in a statement.

Ryanair added that BAA had doubled its passenger charges despite suffering a 30 percent decline in business, making Stansted airport uncompetitive.

A BAA spokesman said: "Ryanair doesn't pay a penny more than the regulator allows, and less than they would pay at Gatwick. The charges Ryanair are referring to have been scrutinised by the Competition Commission and comply with the price cap set by the CAA. They have also been in place for two years. We do not believe Ryanair has any case for legal action."

BAA was last week told by the Competition Commission that it must begin selling off Stansted airport and one of its Scottish hubs. The company is looking to challenge an order with an application to the UK's Competition Appeal Tribunal.

"It is interesting that the timing of Ryanair's current complaint coincides with the public debate about whether the Competition Commission's decision to force the sale of Stansted is the right one," BAA added.

Earlier on Wednesday BAA reported an adjusted pretax loss of 116.9 million pounds in the first six months of the year, down from a loss of 167.4 million pounds in the same period of 2010.

(Reporting by Rhys Jones; editing by Matt Scuffham)

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