DAVID Cameron was urged to "be a leader" by a senior Tory last night and to start putting Conservative values at the heart of government.

The MP predicted the Prime Minister would be given a "rough ride" at the upcoming party conference, where supporters of a third runway at Heathrow are planning to make a concerted bid to change Mr Cameron's mind.

It followed remarks by Tim Yeo, chairman of the Commons Climate Change Committee, who said: "The Prime Minister must ask himself whether he is a man or a mouse," adding: "Does he want to be another Harold Macmillan, presiding over a dignified slide towards insignificance? Or is there somewhere inside his heart - 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."

Last night the source told The Herald: "Tim Yeo's 'man or mouse' remark was one hell of a challenge to the PM but a lot of people were urging him on because he is right. We need a third runway at Heathrow to help trade and the welfare of our country."

The backbencher also said Justine Greening should be moved as Transport Secretary in the forthcoming reshuffle, possibly as early as this weekend.

"David needs to be a leader. This is now a real test for him. Struggling to keep the Lib Dems on board has not worked. The Heathrow issue is another sop to Nick Clegg," added the MP.

"What we want from David is leadership on Conservative values. He'll get a rough ride at conference but I want and expect he'll come through. But he has to start listening to us more. The pendulum has to start swinging back our way."

Mr Yeo's decision to question the Prime Minister's "sense of mission" reveals how, for some Conservatives, Mr Cameron has – post the omnishambles budget, post the collapse of Lords reform and post the death of boundary changes – become vulnerable or weak.

Tim Montgomerie, founder of conservativehome.com, said: "Tim would not have raised the possibility of changing his position if David Cameron was not movable on some issues; jelly rather than steel."

Tory MP Conor Burns, who resigned as a Parliamentary Private Secretary to Owen Paterson, the Northern Ireland Secretary, warned "our remorseless drive is not on delivering on the things that matter to them [the electorate], like the cost of feeding their families, hearing their homes and filling up their cars. That's where elections are won."

As Chancellor George Osborne sticks to Plan A and sees his ratings plummet in the process, the Tory leadership's claim of economic competence is being challenged even from within.

Mr Cameron's reshuffle and the party conference will be a chance to reassert himself and the Government.

However, Deputy PM Nick Clegg stressed the Lib-Con partnership would stick to the Coalition Agreement, which says the Government will cancel the third runway at Heathrow and refuse permission for additional ones at Stansted and Gatwick.

Liz Cameron, chief executive of Scottish Chambers of Commerce, said: "A UK hub is crucial to drive our tourist industry and to market Scotland and the UK as a connected place to do business."