A Thames Estuary airport would not be commercially viable and would require a substantial public subsidy, according to a report prepared for the House of Commons Transport Select Committee.
The report claims it would be a "risky investment", because its investment value is "significantly negative", and an investor would be likely not to touch the project.
The transport committee, which is conducting an inquiry into the UK’s aviation strategy, commissioned economic consultants Oxera to carry out the study into the commercial viability of a new airport.
It concluded that a new hub airport would cost in the region of £20?billion to £50?billion.
Designed by Sir Norman Foster and nicknamed 'Boris Island', because of the Mayor's strong support for the project, the proposed airport could provide four new runways to meet demand for extra air capacity in the capital. But it's opposed by environmental groups.