DAVID CAMERON was today told to be “a man” by a fellow Tory MP who believes the Prime Minister can prove his masculinity by giving the thumbs up to a third runway for Heathrow airport.

“The prime minister must ask himself whether he is a man or mouse,” said Tim Yeo MP, who was once a prominent opponent of the third runway, but who now backs expansion on the grounds that new generation aircraft will be more environmentally friendly than the current crop.

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

But the woman in charge of aviation, Transport Secretary Justine Greening, has long been a strong voice against the third runway, partly because her constituency – Putney, Roehampton and Southfields – is right under Heathrow’s flight path.

Also against Heathrow expansion is London Mayor Boris Johnson, who has championed the so-called ‘Boris Island’ concept of a brand new mega-airport in the Thames Estuary.

Greening appeared to back Johnson’s plans today and threatened to resign – she said it would be “very difficult” to stay in cabinet- if Cameron took Yeo’s mano-a-mano advice.

“We need to look long term, start to be more bold, and think what our country needs in 30, 40, 50 years’ time,” she said.

Meanwhile, other recent reports suggest Cameron and Chancellor George Osbourne have already come over to the Heathrow expansion side of the debate.

In other words, we have all the ingredients for all-out civil aviation war in the Tory party and that’s before you bring in the Liberal Democrats, who oppose the third runway.