George Osborne and Boris Johnson, the two frontrunners to succeed David Cameron, intensified their battle on Wednesday as the government prepared the way for a U-turn over a third runway at Heathrow.

Sir Howard Davies, the former director general of the CBI, has been appointed by the government to chair a commission that will allow the Tories to ditch their opposition to a third runway if it rules in favour of expansion at Heathrow.

Osborne, who has been the driving force behind the Tories' change of heart on airport expansion, has advocated the commission as a way of building a cross-party consensus on airport expansion. Most Tories believe the commission is designed to give the Tories cover for abandoning one of their most high-profile pledges at the last election.

The chancellor showed his determination to keep his options open when he played a leading role in forcing the removal as transport secretary of Justine Greening in this week's reshuffle.

Greening, MP for Putney – which lies under the Heathrow flight path – is a fierce opponent of a third runway. She has been replaced by Patrick McLoughlin, a Derbyshire MP, who would have no difficulty in supporting a third runway.

Boris Johnson, who rallied to the defence of Greening on Wednesday, described the commission as a "fudgearama". The London mayor told Radio 4's The World at One: "It's just a fudge, it's just a fudgearama and it's just an excuse for a delay – there's almost three years to run until 2015. If such a commission were not to report until after the next election we'd have lost a huge amount of time. I don't think British business would be remotely satisfied with that answer.

"Noise pollution around Heathrow already affects about 750,000 people. Almost a third of the noise pollution in the whole of Europe from aircraft is felt around Heathrow airport. It is just madness to continue to expand [Heathrow] in West London.

"There are very very good solutions. What I worry about is that we are now seeing a stealthy U-turn carried out which I don't think is in the interests of London or indeed of the country as a whole. In the end you can expand Heathrow, you can put in another runway – actually it will be a short runway – but you have to come back in 10 years' time and do another. In the end Heathrow can't satisfy the country's needs as the principal hub airport."

The Davies commission is not expected to produce its final report until after the next general election in 2015. This will allow the government to uphold the coalition agreement which ruled out airport expansion in this parliament.

But Osborne confirmed at the weekend that he now favours an extra airport in the south of England to ensure that Britain can maintain its hub status and improve links to regional cities in emerging markets such as China. The chancellor officially has an open mind on where to build the extra runway. But it is an open secret that he believes Heathrow is the only realistic venue because it is Britain's only world hub airport.

A delay in making a decision is also designed to avoid a parliamentary byelection in the marginal seat of Richmond Park. Zac Goldsmith, the environmentalist who was elected to the seat in 2010, confirmed that he would trigger a byelection if the Tories embark on a U-turn.

Goldsmith told the Today programme: "We haven't just lost Justine Greening from this department, we have also seen Theresa Villiers moved out, both of whom were absolutely rock solid on this issue in terms of defending what is still the government's line officially. I think their movement out of the Department of Transport shows the government is at least trying to open the door to the possibility of a third runway."

The Tory leadership is keen to avoid a byelection in such a swing seat in London where the party must perform better at the next election if Cameron is to secure an overall parliamentary majority. But the leadership is braced for a battle with Goldsmith at the next general election if the party embarks on a U-turn in its manifesto.

The leadership may also have a battle with Greening, who said before her demotion to the post of international development secretary that she would find it difficult to remain in the cabinet if the party changed its position on Heathrow. Amid fears that Greening could cause trouble in future the leadership started undermining her on Wednesday.

One No 10 source told the Spectator: "She'll have plenty of time to think about runways as her flight to the next developing country circles the airport yet again."

Boris Johnson's support for Greening and his repeated attacks on Downing Street shows that the London mayor has decided to make Heathrow one of his main dividing lines with Osborne. The London mayor favours a new airport on what is being dubbed "Boris Island" in the Thames Estuary.

Johnson told the BBC: "Downing Street is very cross. I am not criticising David who I like and admire hugely. A lot of people think there is going to be a U-turn and that they are gearing up to ditch the commitment against the third runway."