The UK must cut its greenhouse gas emissions by at least 34 per cent by 2020, the committee set up to advise the Government on climate change recommended today.
The Committee on Climate Change, chaired by Adair Turner, also said emissions should be cut by even more if an international deal on reducing greenhouse gases is agreed.
If the current UN negotiations lead to a new deal on climate change in Copenhagen next December, the UK's greenhouse gases should be cut by 42 per cent on 1990 levels by the end of the next decade.
The significant reductions can be achieved at a cost of less than 1 per cent of GDP in 2020, and using existing green technologies, a report from the committee said.
But stronger Government policies will be needed to move the UK to a low-carbon economy.
The cuts can be achieved by cleaner power generation from sources such as wind, which could make up 30 per cent of the UK's electricity by 2020, and measures including energy-efficiency improvements in homes and offices and developing more efficient, electric and hydrogen-powered cars.
The report said nuclear power could play a role in low-carbon electricity generation, and did not rule out new conventional coal-fired power stations in the next decade.
It recommended the Government should make clear that fossil-fuelled power plants which do not have technology to trap and permanently store carbon emissions should not be allowed to generate electricity beyond the early 2020s.
New coal-fired power stations should only be built with the "clear expectation and certainty" that they should be retrofitted with carbon capture and storage (CCS) by the early 2020s, Lord Turner said.
The climate change committee, set up under the Climate Change Act, has already recommended a cut of 80 per cent on 1990 levels by 2050 - advice which has been accepted by the Government.
Today's report set out the first three five-year "carbon budgets" needed to meet the interim and long-term reductions in emissions.
The committee said the budgets should include all greenhouse gases, not just carbon, but should not include aviation and shipping because of difficulties in deciding how much the UK is responsible for.
"Clear strategies" should be in place to cut emissions in those areas, the report recommended.
The report also said the 34 per cent target should be achieved by emissions cuts domestically and within Europe, and not through "offsetting" by paying poor countries to reduce their greenhouse gases.
Lord Turner said: "Climate change poses a grave threat to human welfare, the environment and the economy.
"We need to act now, in the UK and as part of a global agreement, to significantly reduce our emissions.
"It is not too late to tackle climate change, but it will be unless the world takes action soon, and the developed countries need to lead the way with strong commitments and strong delivery against the budgets.
"The reductions required can be achieved at a very low cost to our economy: the cost of not achieving the reductions, at national and global level, will be far greater."
He acknowledged that the higher electricity and gas prices created by investment in renewables could push a further 1.7 million households into fuel poverty - but said 400,000 could be lifted out by energy efficiency measures in their homes.
Lord Turner said the kind of changes ordinary people would see as the UK implemented emissions reductions included better insulated homes, replacement of conventional light bulbs with low-energy and LED alternatives, and more plug-in and hybrid electric cars on the roads.
Parking meters could even be installed with plugs for recharging vehicles, he said.
The energy-saving policies in the report were welcomed by Philip Sellwood, chief executive of the Energy Saving Trust, who called for a long-term strategy from the Government to reduce power use.
He said: "Along with a rapid rollout of Smart Meters and fixing feed-in tariffs, micro-generation will become an affordable reality.
"Ongoing investment in the advice we give to householders and communities to help them make best use of the help on offer will mean that an 80 per cent reduction in household carbon emissions by 2050 is achievable.
"All of this will help individuals play their part in carbon targets without making austere lifestyle changes."
Lord Turner said a major part of meeting the emissions reductions would come from "de-carbonising" the energy sector, with 40 per cent cuts from electricity generation needed in the next 15 years.
Despite concerns about the unreliability and costs of wind power, he said it would play the most important role in moving towards renewable energy generation, while the report said there was also a "strong economic case" for nuclear power in the UK.
Lord Turner said he was not going to comment on individual investments by individual companies - such as E.ON's plans to build a new coal-fired power station at Kingsnorth, Kent.
But he said: "We can't have coal-fired power stations going ahead without the clear expectation they will be retrofitted by the 2020s with CCS."
The Lib Dems warned that the recommendations could give the go-ahead to new "dirty" coal-fired power stations which are not fitted with carbon capture and storage technology.
Liberal Democrat climate change spokesman Steve Webb said that "could completely undermine Britain's position on climate change".
"It is simply too high a risk to allow new coal plants like Kingsnorth on the basis of the promise that its carbon emissions will be captured at some point in the future.
"The UK needs to make dramatic strides on energy efficiency, supporting renewables and reducing our dependence on fossil fuels. We should not go ahead with unabated coal."
But conservation charity WWF-UK's head of climate change Keith Allott said: "The committee makes clear that new coal power stations without full-scale carbon capture and storage have no place in a climate-safe future.
"The Government must now accept that approving coal stations such as Kingsnorth, which do not have this in place from the outset, is simply not an option.
"The introduction of an emissions performance standard, limiting emissions from power stations, would help to prevent this from happening."
Energy and Climate Change Secretary Ed Miliband said moves to reduce emissions would not just bring about changes in policy but a "revolution in thinking" in which all important decisions would have to take account of the carbon budgets.
"For every major Government decision, we will be able to tell if it fits the budget, if emissions savings have to be made elsewhere, or whether it simply can't be done."
And he said: "Plotting a course to a low-carbon future here in the UK is vital if we are to reach our domestic goals and reach an international agreement.
"Carbon budgets will set our trajectory and send out a clear message that we will tackle climate change here in the UK."
The Government will set the first three legally-binding five-year carbon budgets alongside the fiscal Budget in the spring and will publish its full response to today's report next summer.
The committee's report was published as negotiators began the latest round of international climate change talks in Poznan, Poland - with the aim of achieving a new global treaty on cutting emissions next December in Copenhagen.
EU ministers are also hoping to secure an energy and climate change package in the next two weeks which will commit Europe to emissions reductions, renewable energy expansion and the development of carbon capture and storage technology.
WWF's Dr Allott said: "Committing to cutting the UK's emissions by 42 per cent by 2020 would set a world-beating target and inspire hope that we can still head off the worst impacts of climate change.
"Even better, Lord Turner has confirmed that this is both achievable and affordable. Now the Government must offer an immediate signal that it will accept this target.
"By doing so, it would inject some much-needed ambition into the climate change negotiations currently taking place at both EU and UN level."
Friends of the Earth urged the Government to block plans for new coal-fired power stations and airport expansion.
The environmental group's executive director Andy Atkins said: "We're delighted that the committee recognises that UK greenhouse gas emissions must be slashed by 42 per cent by 2020 if we are to play our part in avoiding catastrophic global warming - but this must not be conditional on reaching an international deal.
"The committee clearly acknowledges the major threats that aviation and coal pose to our climate change targets, but it has fudged the question of what the Government must do.
"Ministers must scrap plans to allow UK airports to expand and not allow any coal-fired power stations to be built without carbon capture and storage."
And he said: "Lord Turner's strong backing for urgent investment in green energy and cutting energy waste hits the nail on the head.
"This will not only cut emissions, it will create exciting business opportunities, new jobs and a safe, clean and prosperous future for us all."
John Sauven, executive director of Greenpeace, said: "Assuming the Government accepts the advice of its own climate change committee, Kingsnorth is dead in the water.
"E.ON's investors and the company's executives will read the Turner report with sweaty palms, as their coal plans don't even come close to satisfying the new standards the committee is demanding."
He went on: "The quickest, cheapest and fastest way to slash emissions and meet the country's energy demands is to invest in efficiency, renewable energy and super-efficient combined-heat-and-power plants on the Scandinavian model.
"The Government should adopt Turner's suggestion of tough emissions standards for power stations that would ensure only cleaner technologies are used to power Britain, while ruling out the dirtiest fuels like unabated coal."
The World Development Movement said Mr Miliband must now prove the UK is serious about tackling climate change by saying no to a new coal-fired power station at Kingsnorth that does not have full carbon capture and storage technology.
Tim Jackson, economics commissioner at the Sustainable Development Commission, warned that the Goverment's commitment to building a low-carbon Britain was woefully inadequate.
"The only appropriate response to both the current economic crisis and the impending crisis of climate change is a comprehensive programme of investment in low-carbon technologies and upgrading Britain's buildings," he said.
"What we need is a wholehearted political and economic commitment to achieving a sustainable Britain."
Shadow energy and climate change secretary Greg Clark welcomed the "stretching" targets in the report, but said the Government had a long way to go to meet them.
"Most of the UK's progress on emissions reduction comes from the 'dash for gas' in the 1980s and 1990s; since 1997 carbon emissions have fallen by only 1 per cent.
"The absence of a Government energy policy over the last 10 years has made the decisions now needed more urgent and disruptive than they need have been.
"In this context I am deeply concerned by the committee's assessment that up to 1.7 million households could be pushed into fuel poverty by the impact of the proposed carbon budgets," Mr Clark said.
He said British customers were already paying some of the highest fuel bills in Europe because the Government had failed to prepare for the decline in North Sea oil and gas, and British homes were among the least energy-efficient.
"I will be pressing Ministers to act to stop the poorest energy customers being penalised as a result of the Government's own lack of forward planning," he said.