SUFFOLK MP Tim Yeo has stirred up a new political debate within the coalition after calling on the Prime Minister to abandon the government’s objections to a third runway at Heathrow.

The South Suffolk MP said Mr Cameron had to ask himself whether he was “Man or mouse” and urged him to abandon objections to a third runway.

However he later insisted that he remained a firm supporter of the Prime Minister – but said it was sometimes necessary for governments to re-think policies drawn up in opposition when economic circumstances demanded change.

Mr Yeo said: “I think that David Cameron still has a large number of well-wishers in the Conservative Party, of whom I am one.

“I am a supporter of him, but I do want him to say, in what I would think is a very mature way, when circumstances change, when the needs of the country evolve, I am prepared to revisit decisions I made four years ago.

“I think he would have tremendous support both inside Parliament and outside if he is brave enough to do that this month.”

Mr Yeo added: “There’s really every possible argument in favour of it, what it does need is political courage. That’s what I’m calling for.

“I think the opportunity is there, I think there is a sense inside the Government that the tide is turning on this issue, but I would just like to see it happen sooner rather than later.”

He called for Mr Cameron to show “a bit of steel on the economy” and “if the Lib Dems don’t like it then maybe there’s a majority in Parliament without them on this issue”.

In a national newspaper article he had written: “The Prime Minister must ask himself whether he is man or mouse.

“Does he want to be another Harold Macmillan, presiding over a dignified slide towards insignificance?

“Or is there somewhere inside his heart – an organ that still remains impenetrable to most Britons – a trace of Thatcher, determined to reverse the direction of our ship?

“An immediate go-ahead for a third runway will symbolise the start of a new era, the moment the Cameron Government found its sense of mission. Let’s go for it.”

Mr Yeo urged the Prime Minister to show “political courage” and said a third runway could be approved even without Liberal Democrat support.

However Transport Secretary Justine Greening admitted she would find it “difficult” to remain in a Government which backed a third runway at Heathrow.

Ms Greening, a prominent campaigner against a third runway which she fears would directly affect the quality of life of her constituents in Putney, south-west London, insisted there was now a consensus against the development.

She said a third runway would not be “the right thing for Britain” because it would become rapidly outdated and insisted that a wholesale review of air capacity was needed.

Asked whether she could continue to serve in government if a third runway was approved, she said: “I think it would be difficult for me to do that. But I think, at the end of the day, the process I’m about to kick off is one that will see us come up with a much better, longer-term, solution.”

The planned runway was opposed by both the Tories and Liberal Democrats at the general election and the Coalition Agreement between the two parties explicitly cancelled the expansion.

Conservative London Mayor Boris Johnson also opposes a third runway at Heathrow, favouring instead a new airport in the Thames Estuary to the east of the capital.