A House of Commons Transport committee report has rejected the Mayor's plans for a new hub airport in the Thames Estuary - saying the public expense would be too great.
MPs also say transport infrastructure wouldn't cope and wildlife habitats would be affected. Instead, it urges the Government to allow expansion at Heathrow with a third, and possibly fourth, runway.
But not everyone's convinced.
John Stewart from the Heathrow Association for the Control of Aircraft Noise and Louise Ellman from the Commons Transport Select Committee.