But as he delivered a major speech on climate change from Norway's melting glaciers Friday, the question of the minds of most Britons was: have the true blue Tories really gone green, or is it all a stunt?

Since being elected as leader of the Conservative Party in December, Cameron has embarked on a highly visual personal campaign to convince the British public of his environmental credentials. Much has been made of his preference for cycling to work and his intention to install solar panels and wind turbines on his West London home. The Conservative campaign slogan for the forthcoming local elections projects a simple, catchy message of the kind beloved by political PR gurus everywhere: Vote blue, go green.

According to the ruling Labor Party however, Cameron is nothing more than a political shape-shifter, flip-flopping between the preferences of focus groups and the demands of big business as it suits him. Their campaign broadcast is a not-so-subtle elaboration on this theme, depicting a cartoon "Dave the Chameleon" changing through all the colors of the rainbow as he cycles back and forth to the tune of Boy George's "Karma Chameleon."

Cameron's speech from Norway attempted to address one of the few areas of environmental policy on which Labor has been able to attack him -- his opposition to the Climate Change Levy, a system of taxation on the use of energy in industry.

The reason for his call to abolish the levy was that it was not environmentally friendly enough, he said, proposing instead a "more effective" carbon tax which would be based not on the size of businesses' energy bills but on their individual levels of emissions.

After spending Thursday being towed between melting glaciers by a pack of huskies, Cameron, speaking in Oslo, promised to lead "a green revolution" and urged people to "get positive about climate change."

Tackling climate change would require "genuinely fresh thinking," he said.

Cameron expressed his commitment to a binding, targets-based international agreement to replace the Kyoto Protocol in 2012, and challenged Prime Minister Tony Blair, who has indicated he may be coming round to the U.S. view that national targets are not an appropriate way forward, to do the same.

He said: "Without the incentive provided by political frameworks and international agreements, the investment needed in new technology will not come fast enough on a sufficient scale."

One possibility mooted was a new carbon-pricing framework to encourage investment in clean technologies through taxation.

"We must not be afraid of using the tax system and market mechanisms to encourage investment in, and take up of, clean new technologies which will transform the way we do business, create new markets, and reduce our impact on the planet," he said.

But critics questioned whether Cameron's good intentions would ultimately withstand the demands of big business, with which Conservative policies have traditionally been aligned. And while environmental groups welcomed the sentiments of the speech, they noted the absence of detail.

Cameron is not the only prime-ministerial hopeful vying for the green vote. As he headed to Norway, Chancellor of the Exchequer Gordon Brown, Blair's likely successor, jetted to New York to urge international action against climate change.

Brown chose the United Nations as the forum in which to flaunt his green credentials, delivering a speech in which he called for a "global consensus" to ward off the looming environmental crisis.

In an implicit response to U.S. insistence that economic growth is the key to tackling climate change, he insisted that green policies were essential to securing future growth and prosperity.

The Intergovernmental Panel on Climate Change had estimated that a temperature rise of just 2.5 degrees could cost up to 2.5 percent of global GDP, he noted.

The chancellor continued his theme in Washington Friday, where he urged G7 nations to support alternative sources of energy and improve energy efficiency.

But back in Britain, environmental groups expressed skepticism. Brown's words were at odds with his record on climate change, which had in fact been deeply disappointing, they said.

"We are delighted that climate change is at the top of the political agenda," said Tony Juniper, executive director of Friends of the Earth. "But it will require more than warm words to tackle the problem. U.K. emissions are rising, despite promise of substantial cuts."

While it was encouraging that Brown had made climate change a major theme of his U.S. trip, he had not given the issue sufficient priority at home, he said. His annual Budgets had "merely tinkered in the margins," green taxes had fallen under his chancellorship and emissions had risen, he continued, asking: "Will the chancellor move beyond words and deliver the substantive policies needed?"

Similarly, Cameron was helping to make the environment a key political issue, but had yet to come forward with substantive policies, Juniper said.

"Mr. Cameron must show that he is prepared to take on the vested interests from industry, and the aviation and motoring lobbies and spell out his blueprint for a safe, sustainable and successful economy," he concluded.

The Green Party's principal speaker, Keith Taylor, commented: "Combating climate change needs action, not words. Chasing the headlines with visits to Norway or grand speeches at the United Nations does not deliver an ounce of carbon reduction."

Cameron, and Brown, are tapping into a vein of new-found public concern about climate change and its potential impact. However they both have a long way to go to convince skeptical voters that their intention is to secure tangible environmental results, and not just victory at the ballot box.

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