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"Transport topped the agenda when the four main candidates to be London mayor clashed at a hustings in the City.
"Conservative Boris Johnson attacked Ken Livingstone for his promised Tube fare cut, but the Labour candidate accused him of "sitting on money" rather than helping hard-pressed commuters.
"Lib Dem Brian Paddick urged 'smarter' use of Heathrow to increase capacity, while the Greens' Jenny Jones suggested a congestion charge around the airport.
"The election will take place on 3 May."