The UK's House of Commons Transport Committee has rejected proposals by London Mayor Boris Johnson to build a new four-runway hub on reclaimed land in the Thames Estuary.
Committee chairwoman Louise Ellman says the plan, dubbed Boris Island, would require "huge public investment" and could have a "substantial potential impact" on local wildlife.
It would also necessitate the closure of the UK's existing main hub, Heathrow airport, which she says would have "unacceptable consequences" for the local economy in west London.
Throwing its weight behind proposals to expand Heathrow instead, the committee concludes that a third runway is "necessary" and a fourth "may have merit" - particularly if located in less populated areas to the west of the airport.
Britain's Coalition government has been widely accused of dithering over Heathrow expansion, with Prime Minister David Cameron of the Conservative Party saying no decision will be taken until 2015 at the earliest.
His coalition partners, the Liberal Democrats, have vowed to block any support for a third runway, which has been ruled out by both the Conservative Party's manifesto and the Coalition agreement.
Endorsing arguments put forward by Britain's business lobby that the UK economy will suffer without more capacity in the south-east, the Transport Committee describes the current situation as "unsustainable".
"A two-runway hub airport [at Heathrow] is not adequate for the needs of the UK," it concludes. "We have considered the options put to us and on the basis of the evidence we have heard we recommend that the government allow Heathrow to expand."
The government has not committed to implementing its findings, and Mayor Johnson has already reiterated his strong support for the Thames Estuary proposal.