Calling on the prime minister to "take control" of the chancellor, George Osborne; energy minister, John Hayes, and other Conservatives known to be sceptical of renewable energy and climate change targets, David Nussbaum, the chief executive of WWF-UK, said: "On becoming prime minister, Cameron suggested he would be the fourth minister at the Department of Energy and Climate Change (Decc) and that his would be the 'greenest government ever'.

"But he seems to have lost his voice. There is currently a complete breakdown in government energy and climate change policy, sending mixed signals to investors and undermining job creation. [His] continued silence would be a betrayal not just of election promises, but of the UK national interest."

Nussbaum's call came as the cabinet remains split over energy policy. The Liberal Democrat energy and climate change secretary, Ed Davey, has insisted the government backs a shift to a low-carbon economy through the development of renewable energy and new nuclear power, while the Osborne has shown support for a generation of new gas-powered plants.

The much-delayed energy bill is now expected by the end of November. Davey and climate change minister Greg Barker are due to attend the global climate talks in Doha, which begin on 26 November.

Cameron positioned himself as an environmental enthusiast after he visited Norway in 2006, in a visit organised in part by WWF to witness climate change firsthand and famously hugged a husky dog. But although he pledged to lead the "greenest government ever" shortly after taking office and was key in delivering the Climate Change Act that legally committed Britain to making deep emission cuts, he has since appeared to row back his enthusiasm for low-carbon policies.

"It's time for Cameron to be the prime minister he told us all he would be and deliver on his earlier promises," said Nussbaum. "His lack of vocal leadership on climate change and energy is jeopardising some of the most promising green shoots of recovery. The UK needs significant investment in green infrastructure, yet he is letting a rogue pack within his party play politics with such an important issue."

According to WWF, Osborne and Hayes have "significantly" undermined investment confidence in the renewable energy sector. "Several major companies have already shelved their planned investment in the UK's renewable energy supply chain whilst others are reconsidering their future investment due to the political risk and lack of certainty created. Yet ironically, the CBI has repeatedly said that the green economy and the renewable energy sector are among the few bright spots for economic recovery in the UK, offering substantial potential for jobs, exports and investment."

WWF called on Cameron to resolve the deadlock and bring his government together behind a strong energy bill. "Much of the UK's ageing power infrastructure needs replacing. As well as a challenge, WWF and other organisations like the CBI see this as an opportunity for the UK economy. If the prime minister acts decisively he could move the UK towards a carbon-free, resilient energy future, with a growing number of highly skilled UK jobs and growing investment. This is the time for the government to speak with one voice in favour of green infrastructure, and the prime minister should provide it," said Nussbaum.

In a separate move, MPs on the powerful environmental audit committee called on Osborne to reassure investors that the Treasury is committed to the move towards a greener economy.

The chairwoman of the cross-party committee, Joan Walley, said: "The Treasury must end the uncertainty on energy policy and give investors and businesses the confidence to seize the enormous opportunities presented by new clean technologies. A second 'dash for gas' could lock the UK into a high-carbon energy system that leaves us vulnerable to rising gas prices.

"The government needs to reassure investors by setting a clear target in the energy bill to clean up the power sector by 2030."