The UK's greenhouse gas emissions are not falling fast enough to meet government targets, say advisers.
Emissions rose by 3% during 2010, says the Committee on Climate Change (CCC).
This was due to extra energy demand in cold weather; but the general trend is flat, which is "incompatible" with the 3% annual cuts needed, the CCC says.
Energy Secretary Chris Huhne said the government's once-in-a-lifetime reforms showed it was serious about making the changes "vital to cut emissions".
The CCC's report says people are buying less polluting vehicles and installing more efficient boilers, but progress on home insulation is slowing.
The government has formally adopted five-yearly sets of emission targets - "carbon budgets" - proposed by the CCC.
Emissions for 2010 were within budget - but that was mainly due to the recession, which lowered economic activity and therefore emissions during 2009.
"During 2010, the economy grew by 1% but emissions stayed flat," the committee's CEO David Kennedy told BBC News.
"If we move to 2% growth per year and above, it's uncertain what would happen - would emissions go up or stay flat? - we don't know.
"But as we return to growth, we will have to do better."
Emissions of carbon dioxide rose during 2010 - partially offset by a fall in output of other greenhouse gases such as methane.
This suggests that existing policies have not broken the historically close relationship between economic growth and CO2 emissions.
"This is the third progress report from the CCC, and each one has said that a step change is needed," commented Keith Allott, head of climate change with environment group WWF-UK.
"The government now has no excuses for failing to listen. The UK urgently needs clear, stable and strong policies that will unlock the potential of the low carbon economy."
Mr Kennedy said that the government must adopt new tools in order to make emissions fall by 3% per year - the rate needed in order to stay with the successive carbon budgets, which is a legal requirement.
"In terms of insulating cavity walls we've done virtually nothing to date, and there's been very little progress in terms of changing consumer behaviour in transport," he said.
"The government should set a clear goal, such as insulating all lofts and all cavities within five years, and this should be reflected in an obligation on energy companies to deliver on these targets."
These obligations could be made as part of the "Green Deal", the proposed scheme under which companies will install insulation in people's homes using financial mechanisms that carry no up-front cost and save money in the long term.
The Green Deal is supposed to be up and running late next year.
Government proposals suggest that "millions of people could benefit" - but do not set firm targets.
The number of lofts and cavity walls insulated by professionals fell by 30% in 2010.
The committee also noted that only 2% of heating is supplied from renewable sources, while projections indicate 12% is needed by 2020.
However, average emissions of new cars fell from 149.5 grams of carbon dioxide per kilometre (g/CO2/km) in 2009 to 144.2g/CO2/km in 2010 - a faster fall than the committee had projected.
Another key element the CCC identifies in bringing emissions down at the required rate is reforming the electricity market, an area where the government is expected to publish firm proposals within the next few weeks, following a recent consultation.
Mr Huhne said the required policy changes were in hand.
"As we come out of recession, the coalition is determined to reduce our reliance on fossil fuels, which means a permanent shift to low carbon has to be locked into our economy in good times and bad," he said.
"The coalition's once-in-a-generation reforms of the electricity market, the Green Deal and the Green Investment Bank show we're serious about making the long term structural changes that are vital to cut emissions and keep the lights on."
Earlier in the week, Mr Huhne had commented that energy prices in France were rising more slowly than in the UK because of much lower French dependence on fossil fuels for electricity generation.
But Rhian Kelly, director for business environment at the Confederation of British Industry (CBI), said recent policy changes had slowed decarbonisation.
"Recent policy shifts have dented investor confidence, such as the sudden removal of the incentive behind the Carbon Reduction Commitment.
"To get back on track, the government must clarify a number of grey policy areas, including the Green Deal, electricity market reform and the Green Investment Bank."