The Cabinet re-shuffle has put Boris Johnson on a collision course with the government over Heathrow.
The Prime Minister has removed the Putney MP Justine Greening as Transport Secretary.
London mayor Boris Johnson has attacked the demotion of Justine Greening in the Cabinet reshuffle - claiming it shows the Government is intent on what he calls the "simply mad" policy of a new runway at Heathrow Airport.
The influential Conservative said he would fight any moves to build a new runway at the busy London terminal "all the way" and accused ministers of failing to be straight with Londoners.
Ms Greening, whose Putney constituency lies under Heathrow flightpaths, has been a vociferous opponent of a third runway.
And that stance appeared to lie behind Prime Minister David Cameron's decision to shift her to the international development brief and replace her with ex-chief whip Patrick McLoughlin.
Downing Street insists the Government's position is unchanged since the coalition agreement of 2010, which committed ministers to scrapping extra runway plans drawn up under Labour.
But it has launched a consultation process on future airport capacity and Chancellor George Osborne sparked speculation over a possible U-turn by saying he believed more runway capacity was needed in the south-east of England and all options should be examined.
Mr Johnson, widely seen as a challenger to Mr Cameron to be the next Conservative leader, said Ms Greening has been "a first-rate transport secretary".
Mr Johnson said that a new four-runway airport should be built instead, preferably to the east of London, to address the growing need to expand the UK's aviation capacity.
The switch of Ms Greening was attacked as a "panic" measure by Tory MP and environmental campaigner Zac Goldsmith.
Mr Goldsmith has already said he will not be a Tory candidate at the next general election if the party does not explicitly oppose a third runway for Heathrow.