The government should reject the "Boris Island" Thames Estuary airport plan and expand Heathrow instead, a report by MPs has said.
Mayor of London Boris Johnson has argued for a new hub airport in the Thames Estuary.
Yet the House of Commons Transport Committee warned it would be hugely expensive.
The mayor insists London needs a new airport and the only possible place is east of London.
But the report also warned the new airport could mean the closure of Heathrow and could harm estuary wildlife.
The MPs argue a third runway at Heathrow is necessary instead and even suggest a fourth runway might have merit.
A third runway is opposed by both residents and councils in west London.
The committee said adding new runways to expand other existing airports
was not a long-term solution.
Committee chairwoman Louise Ellman MP said: "Research we commissioned made plain that building an entirely new hub airport east of London could not be done without huge public investment in new ground transport infrastructure.
"Evidence to our inquiry also showed a substantial potential impact on wildlife habitat in the Thames Estuary.
"The viability of an estuary hub airport would also require the closure of Heathrow - a course of action that would have unacceptable consequences."
Mr Johnson said: "The committee is bang on the button in saying we need a proper hub airport.
"But, by suggesting that Heathrow should double its runways from two to four, the committee is putting four fingers up to hundreds of thousands of Londoners.
"London and the wider UK do need a hub airport that can operate 24 hours a day without constraint and the only place that is possible is to the east of London."
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