The project to construct a highly controversial third runway and a sixth passenger terminal at Heathrow, the most congested airport in Europe, could cost about £9bn, the Civil Aviation Authority has said. Financial Times

It would be the largest single investment made by BAA since the UK airports group was privatised in 1987 and would be double the £4.5bn being spent on Terminal 5, due to open in late March.

The government is launching a public consultation into the further expansion of Heathrow, which is expected to trigger a wave of opposition from environmental campaigners and local authorities and residents groups.

Government proposals are expected to include changes to long-standing operating procedures at Heathrow, which in a first stage could add 10-15% to take-off and landing capacity on the existing two runways, but at the cost of a higher noise burden on local residents.

The eventual building of a third runway, which is unlikely to be in operation before 2020 at the earliest, and a sixth terminal, could ultimately raise passenger capacity to 120m a year compared with current volumes of more than 67m.