Labour's London mayoral candidates clashed in a furious row last night over whether to build a third runway at Heathrow.
Sadiq Khan told a hustings in Westminster that there should be no third runway because of the dangerous levels of pollution it would cause.
"Our air is illegal," he told the Prospect hustings.
"We are breaching EU directives. Last year 4,300 people died as a direct result of our air quality. A third of children's lungs aren't being developed in our inner city."
He called for a "better Heathrow not a bigger one," adding that Gatwick should be expanded instead.
His comments followed an interview with the Evening Standard in which he accused his rivals David Lammy and Tessa Jowell of being "ultra-Blairite" for supporting a third runway at Heathrow.
But in a furious response Lammy accused him of playing the "same old politics of Ed Miliband".
"Absolutely we have got to get on and do something.
"But we should not play politics with this issue. Sadiq was for Heathrow expansion in 2008. He was for it when he was transport secretary in 2009. He was for it on the Sunday Politics just a few months ago. Zac Goldsmith announces he's running and suddenly he's against it. I think it's important to be straight with people and not play the same Ed Miliband politics that got us nowhere."
Rival candidate Gareth Thomas said there should be extra runways at both Heathrow and Gatwick while Tessa Jowell said she would wait for the Davies Commission report on airport expansion before saying where it should take place.
"We can't go on forever putting this decision off because it's just too difficult," she added.
Diane Abbott and Christian Wolmar were the only candidates to speak out against airport expansion in the south east.
The entrance of the Tory anti-Heathrow expansion campaigner Zac Goldsmith into the race to be the next London mayor has made it a major electoral issue for the first time. All the leading candidates in previous mayoral elections have opposed a third runway at Heathrow.
Khan's campaign believe Labour will lose if their mayoral candidate supports expansion.
"It's impossible to win London while backing Heathrow expansion," a source close to Khan told Politics.co.uk.
"If Jowell wins the nomination, Goldsmith will use her support for Heathrow against her and she will lose."
However, Khan's opposition is likely to upset two of the unions who are currently supporting him. Both the GMB and Unite back a third runway.
There is also a large business lobby in favour of expansion.
Writing in the City AM newspaper today about his opposiion to a thrid runway, Khan claims that "competition between two primary airports will be better for Londoners, better for businesses and better for passengers."