Yet, in recent months, there have been some signs the Tory leader's passion for the green cause has cooled, that it may have served its purpose of illustrating change, so he is reverting to more traditional Tory tunes such as law and order. Green campaigners smelt a rat in May after Mr Cameron failed to mention the words "environment" or "climate change" in a 1,200-word statement about his priorities for government.
The party leadership denies it has diluted its commitment to the environment and has been working hard to reassure its new green friends. Mr Cameron and the shadow Chancellor George Osborne have made "green" speeches in the past six weeks, which steadied some nerves. Mr Osborne's address to the Green Alliance played particularly well. Yet some environmentalists believe the Tories are doing only what they judge necessary to head off attacks by green groups.
The missing piece of the Tory jigsaw is its commitment to green taxes. Officially, the Opposition remains committed to raising green taxes and putting "every penny" raised into a "family fund" that would cut taxes paid by families. Mr Cameron insisted: "The truth is: it's not that we can't afford to go green – it's that we can't afford not to go green."
However, it appears such taxes may play a smaller role in trying to change people's behaviour than Mr Cameron and Mr Osborne originally envisaged, with incentives to "go green" playing a bigger part. "Green taxes are taking more of a back seat," one Shadow Cabinet minister admitted. "The problem is it is difficult to talk about raising taxes during a downturn. People think green taxes are stealth taxes because Gordon Brown has given them a bad name."
Another issue of concern for some is that the Tories are warming to nuclear power. Last year, it viewed a new generation of nuclear power stations as "a last resort" but would now support the move if there were no taxpayers' subsidy.
The party's environmental spokesmen, Peter Ainsworth and Greg Barker, and Alan Duncan, the shadow Business Secretary, are believed to be sceptical about an expansion of nuclear. But Mr Cameron and Mr Osborne appear to have overruled them. Private signals have been sent to prospective builders of nuclear plants that they "don't need to worry" about the attitude of a Tory government.
Until the recent wobble, the wooing of the green movement had been highly successful. Pressure groups and think-tanks describe MrAinsworth, the shadow Environment Secretary, as "more engaged" in green issues than government ministers. The Tories led calls for a ground-breaking Climate Change Bill to set a target for cutting Britain's carbon emissions by 2050, and, in a rare coup for an opposition, persuaded the Government to act.
Yet the early hopes raised by Mr Cameron's "vote blue, go green" campaign were always going to be hard to fulfil. A very green blueprint was produced last year by the party's "quality of life" group, led by John Gummer and Zac Goldsmith. Proposals included parking charges at out-of-town supermarket and shopping malls; a moratorium on airport expansion and increased taxes – including VAT – on short-haul domestic flights. Mr Cameron distanced himself from the report, saying it was "to" and not "for" the party, and making clear he would not impose parking charges on the weekly shopping trip.
One green campaigner said "brand Cameron" would be seriously damaged if the Tories did not produce a manifesto that lives up to their rhetoric. "They have symbolic positions on aviation tax, EU efficiency standards and micro-generation, But there is no broader framework to underpin these and other commitments," he said.
While green groups do not doubt Mr Cameron's commitment, they sense a big gap between him and the rest of the party on issues such as renewable energy, and are looking for reassurance.
Steve Shaw, a campaigner at Friends of the Earth, said: "We're delighted that David Cameron seems to recognise the important role green action can play in strengthening the economy, especially at a time of economic instability.
"Ending our fossil-fuel addiction has never been more important. Cameron must increase political pressure on the Government to deliver an energy policy based on fuel efficiency and renewable power. A low-carbon economy will tackle rising costs, generate new jobs - and provide a safer, cleaner future."
John Sauven, executive director of Greenpeace, said: "The Tories are still talking seriously about green issues, that has to be good. But how deep does the environment run in their veins? They've ruled out unabated coal-fired power stations like Kingsnorth [in Kent] but left open the possibility of expanding Heathrow. If they are serious, they must say categorically that there will be no third runway at Heathrow."
Stephen Hale, director of the Green Alliance, said: "David Cameron's environmental speeches cannot be faulted. But the gap between his aspirations and commitments is alarming. It needs to be filled very fast, if the Conservative are to become a credible government in waiting."
Face to watch: Zac Goldsmith
Former editor and now chairman of The Ecologist magazine and son of the late Sir James Goldsmith, the billionaire Eurosceptic. Was vice-chairman of the Conservative Party's quality of life group which produced a set of green policy ideas last year. Has enjoyed a lower profile since then, but Mr Cameron's allies say he remains an influential adviser to the Tory leader. Has good chance of becoming a Tory MP at the next general election, after being chosen as a candidate for Richmond Park. Could emerge as the green conscience of a Conservative government.
Key policy commitments
Emissions
"Cap and trade" scheme to reduce carbon emissions by 60 per cent by 2050; replace climate change levy with a carbon levy.
Energy
No new coal-fired power stations unless they have a carbon capture and storage facility; decentralised energy in towns and cities with small local power stations rather than huge regional ones; German-style feed-in tariffs allowing people who produce their own energy to sell surplus to the grid.
Air travel
Heathrow airport should be made "better, not bigger".
Unanswered questions
* How much would a Conservative government raise from green taxes, such as those levied on domestic flights and the worst gas-guzzling vehicles?
* Would the Tories' traditional Euroscepticism prevent them from effectively taking action at European Union level to combat climate change?
* Would a Conservative government definitely reject proposals to build a third runway at Heathrow airport, despite fears over the effects of air travel on the environment?
* Would the Tories' attitude to the role nuclear power would play in the UK's future energy mix be any different from the current government's?
Tomorrow: Cameron's first 100 days, and Europe
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