By Rhys Jones
LONDON (Reuters) - Britain's transport minister said on Tuesday she would probably resign if the government gave in to pressure to expand London's Heathrow airport.
Conservative Prime Minister David Cameron's government has ruled out building a third runway at Heathrow before the next election, in part to appease the junior coalition partner, the Liberal Democrats, but the issue has returned to the agenda with the economy still stuck in recession.
Government insiders say Cameron and finance minister George Osborne have an open mind on expanding Heathrow but that they were unlikely to reverse their policy before the election, due in 2015.
Transport Secretary Justine Greening was asked by BBC radio to respond to comments by a fellow Conservative, goading Cameron to approve the new runway and show if he was a "man or a mouse".
Asked if she would remain in the cabinet if the government decided to back the airport expansion, she said: "I think it would be very difficult for me to do that."
Writing in the Daily Telegraph, Tim Yeo, who chairs parliament's Energy and Climate Change committee, said backing the third runway would give the government a "sense of mission".
"The prime minister must ask himself whether he is man or mouse," he wrote. "An immediate go-ahead for a third runway will symbolize the start of a new era, the moment the Cameron government found its sense of mission. Let's go for it."
Several options are being considered to increase the southeast of England's strained airport capacity: a third runway for Europe's busiest airport, Heathrow, a second runway at London Stansted, or a new airport in the estuary of the river Thames.
The government blocked development of a third Heathrow runway as it came to power in 2010, to boost its environmental credentials and win the backing of thousands of households who would be affected by increased air traffic over the capital.
Heathrow operator BAA, owned by Spain's Ferrovial, believes the airport is falling behind European rivals like Paris, Frankfurt and Amsterdam in the battle for lucrative routes to China because of the constraints on growth.
The prime minister's spokeswoman said the government would stick to its coalition deal, which rules out expanding London's Heathrow, Gatwick or Stansted airports.
"The prime minister has said that the coalition parties made a pledge not to have a third runway and that's a pledge we will keep. The position is we don't see the argument for a third runway," the spokeswoman said.
Colin Stanbridge, head of the London Chamber of Commerce and Industry, urged the government to "put politics aside" and build a third runway, which he said was the solution to Britain's "short-term capacity crunch".
The government will launch an aviation consultation document later this year
(Additional reporting by Mohammed Abbas; Editing by Robin Pomeroy)