BAA, which owns and operates Heathrow, launched the case it will put forward at the public inquiry into the building of the £1bn terminal, which is expected to be the longest and most complicated of the decade, and is due to start next 16 May.
The airports management company argues that the new terminal is essential to meet increased demand for air travel at Heathrow, already operating at its full capacity of 50 million passengers per year. It forecasts that passengers using London's airports will increase from the current annual level of 75 million to 165 million by 2016.
Terminal 5, whose first stage could be completed by 2002, would provide capacity for 30 million passengers per year. It would have a rail station connecting it with the Heathrow Express, currently being built, and an Underground station.
BAA's technical director, Michael Maine, said the feasibility of rail links to Reading and Slough was being considered, in an attempt to increase from one-third the percentage of passengers using public transport to reach the airport.
Opponents, however, are worried about increasing noise and pressure to increase night flights and say that, while an extra runway has been ruled out now, the debate will be revived once Terminal 5 is built. John Boulton, of the Heathrow Association for the Control of Aircraft, said: "They always want more, just so they can build more shops and make more profit."
The government is studying a report by a Department of Transport committee which examined runway needs in the South-east and is expected to endorse the committee's finding that no new runways are needed for 20 years.