The six Labour candidates hoping to succeed Boris Johnson as mayor of London have clashed over London airport expansion.
Tooting MP and former transport secretary Sadiq Khan set the tone for the debate, following his backing of expansion at Gatwick airport.
He defended his opposition to Heathrow's third runway, saying that London's air quality was already in breach of EU regulations. He said London needs "a better Heathrow, not a bigger one".
Rival David Lammy, the MP for Tottenham, accused Khan of "the same Ed Miliband politics that got us nowhere".
He criticised the timing of Khan's decision, coming after the announcement of Zac Goldsmith as the potential Tory candidate for the 2016 election.
Goldsmith, known for being an environmental campaigner, is opposed to a third runway at Heathrow. Lammy said: "Zac Goldsmith has announced he's running and suddenly Sadiq is against it."
Tessa Jowell, who is currently favourite in the race according to a YouGov poll, said she would wait for the Airports Commission's final report before making a decision.
While Hackney North and Stoke Newington MP also Diane Abbott opposed Heathrow expansion, Harrow West MP Gareth Thomas said new runways should be built at both Heathrow and Gatwick.
The only non-politician in the race, journalist Christian Wolmar, said climate change should inform the decision.