The full environmental impact of expanding Heathrow Airport has been overlooked or underestimated, according to a London Assembly report.
The report claimed projections for noise impact levels were false
The environment committee examined the plans for a third runway and a sixth terminal.
It claimed the economic benefits of expanding the west London airport had been exaggerated and the plans would breach EU air quality standards.
The report comes as London's mayor called for the plans to be dropped.
The committee report also claimed projections for noise impact levels were false.
Darren Johnson, chairman of the environment committee, said evidence from interested groups and individuals, both in favour of and against the expansion, had been considered.
He said: "It is our view that the noise and air quality conditions placed on a third runway and sixth terminal are inadequate and do not take into account the full impact the proposed expansion will have on Londoners.
"Expansion at Heathrow should not be considered while various local and international conditions continue to be overlooked or completely underestimated."
The report concluded that expansion at Heathrow should not proceed until a number of criteria were met, including carrying out a full, independent health impact assessment on local residents.
On Monday, London mayor Ken Livingstone visited the village of Sipson, which is likely to be bulldozed if the third runway plans are given the go-ahead.
"It is vital that all airport expansion in London and the South East, including Heathrow, is halted now, as it is completely contrary to the growing evidence on the role of aviation in contributing towards catastrophic climate change," the mayor said.
"Rather than more runways and plane journeys, we must cut carbon emissions by using energy more efficiently."
The London Assembly's report forms part of the government's public consultation over the third runway.