The report serves another blow to the airport, which has been campaigning for years to be allowed to add a third runway because it is operating at full capacity but faces opposition from some prominent politicians, local residents and environmental groups.
Activists opposed to the expansion of London`s Heathrow Airport blocked an approach tunnel last week by chaining themselves to a parked vehicle, bringing traffic chaos to Europe`s busiest airport.
A government-appointed Airports Commission named Heathrow as the preferred site for a London airport expansion in July, and Prime Minister David Cameron has said he will decide by the end of the year whether a new 23 billion-pound runway should be built there.
Heathrow`s largest shareholder is Spanish infrastructure firm Ferrovial . Other partners include Qatar Holding, China Investment Corp and the Government of Singapore Investment Corp.
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