Green Dave takes his new eco-car for a spin (and tells his environment spokesman the Porsche must go)

David Cameron will tomorrow pose for pictures next to his new government-issue £40,000 hybrid car - but behind the smiles for the camera lurks private grief.

The Tory leader is using his choice of official car for maximum PR advantage, staging a special test drive of his new Lexus GS 450h. No doubt, his transport and environment spokesmen will look on approvingly as Mr Cameron repeats his soundbite that we must all "be the change".

But for Gregory Barker and Chris Grayling, that phrase might strike a discordant note - The Independent on Sunday has learned that both have been forced to sell their private gas-guzzlers.

Mr Barker, Mr Cameron's environment spokesman, waved a regretful farewell to his Porsche Boxster at the beginning of the month. Then, two weeks ago, Mr Grayling, the Tories' transport spokesman, sold his Land Rover Freelander.

They are the latest victims of the political "car wars" raging between the parties as each struggles to be "greener-than-thou".

Gordon Brown's allies lost little time yesterday in pointing out that Mr Cameron's petrol-electric model is larger and more polluting than the Toyota Prius ordered (but not yet used) by the Chancellor.

But Mr Cameron's aides justify his choice by pointing out that the Opposition leader will use his official car for longer journeys than the "run-about" needed to ferry Mr Brown around the Westminster village.

Mr Barker also accompanied Mr Cameron on his recent flight to the Arctic Circle to see global warming in action.