An independent think-tank has issued the government with a "reality check" over its green ambitions.
The report from Cambridge Econometrics warns the government is on course to miss its long-term targets for promoting renewable energy and cutting carbon emissions.
Based on the actions already taken by the government, the report forecasts the government will miss its targets for renewable energy in 2010 and 2015 by a wide margin before narrowly meeting the target in 2020.
The report calls on the government to implement stronger policies if it is committed to tackling climate change.
Professor Paul Ekins, from the Policy Studies Institute, said: "These forecasts provide a reality check to the rhetoric on climate change that is now standard government fare.
"We consistently forecast that the government's 20 per cent carbon reduction goal by 2010 would be missed by a wide margin, but the necessary policy measures were not put in place and the government itself now accepts that it will miss the goal."
But the Department for the Environment, Food and Rural Affairs (Defra) said the researchers had omitted some planned initiatives and insisted it was on course to tackle climate change.
Cambridge Econometrics predicted the proportion of energy obtained from renewable sources would rise to 12.5 per cent by 2015, short of the government's 15 per cent target.
By 2020 it could reach 19 per cent, assuming the price of fossil fuels remains relatively high, putting the 20 per cent target within reach.
The Cambridge Econometrics report follows leaked documents from the Department for Business, Enterprise and Regulatory Reform, in which officials warned the UK would miss targets for renewable energy.
Today's report also found failings in the government's commitment to cut carbon emissions, which is set to become legally binding under the climate change act.
The researchers projected the cut in carbon emissions forecast for 2005-10 would not be enough to achieve a planned 20 per cent cut in carbon emissions.
The government wants carbon emissions to fall below 130 million tonnes of carbon by 2020, but current trends will see them reach nearly 140 million tonnes.
Despite this, the report says the UK should meet its targets under the Kyoto agreement.
Defra insisted the government was on track to meet its carbon emissions goals, thanks to the energy white paper and other ambitious measures.
A spokesman said: "This report does not take account of a number of these measures, such as the carbon reduction commitment and the zero carbon homes initiative, which will help us meet this target.
"We intend to put the 2020 target into legislation through the climate change bill, and the energy white paper provides a strong foundation for a range of policies and programmes that will help us reach it.
"The UK's got a good record on tackling climate change and is already on target to meet and exceed its greenhouse gas reduction targets under the Kyoto protocol."
However, Friends of the Earth (FoE) said it was time ministers and government departments underwent a fundamental attitude shift.
The campaign group called for concrete policies, including requirements for new developments to promote renewable energy.
FoE climate campaigner Mary Taylor said: "The current lack of effective policies is unacceptable. This report shows the need for a robust legal framework in the climate change bill that will oblige the government to reduce emissions by at least 3 per cent year on year.
"We are currently nowhere near that and so are making the job of stabilising our climate more difficult in the long term."
Environmental campaigners have been further alarmed by reports the housing industry is trying overturn the Merton Rule.
The rule requires builders to incorporate renewable energy technologies into new developments, but the Department for Communities and Local Government appears poised to axe it amid pressure from house builders.