Energy policy has moved from a quiet backwater of policy to front-page news. It has been propelled to the top of the political agenda by two colossal challenges we now face: climate change and energy security.

Unless we take action, as Sir Nicolas Stern has said, climate change poses catastrophic humanitarian consequences and economic costs greater than both world wars and the Great Depression combined. And we’ve got to ensure secure energy supplies – we cannot allow ourselves to become overly dependent on imports from less stable parts of the world. We rely on energy to run our economy, to heat and power our homes and to move around. Today, 90 per cent of the UK’s energy is from fossil fuels. The majority of our oil and gas comes from the North Sea, which has peaked in the last few years and is now falling, so we will become increasingly dependent on imported energy.

The energy white paper that I published in May takes critical action to tackle these challenges. First, we must save energy. We are doing more to encourage energy efficiency. We’re introducing a mandatory scheme to cut energy use in the large retail sector – from supermarkets, hotel chains and parts of the public sector. Electronic goods need to be more efficient and we need to phase out low-efficiency light bulbs.

Second, we want to make our energy cleaner. The reform of the renewable obligation will triple renewable electricity over the next eight years. We are helping more micro-generation and distributed generation, for example by making it easier to sell electricity back to the grid and simplifying planning.

Third, we want to get more secure energy supplies, by ensuring a diverse mix of generation and diverse sources of supply. Getting more renewable sources of generation is paramount, and the renewables obligation on generators is crucial. It’s opposed by the Tories – showing again their lack of real commitment to delivering green policies. We also need more import capacity, more storage, better functioning international markets and to maximise access to UK reserves of energy.

Nuclear is controversial, but it has the potential to be one part of the solution. I used to be sceptical about its role, but the facts have changed and many people have changed their minds. The science behind climate change is clear and our dependence on imported energy is growing. That’s why we’re consulting on nuclear power remaining an option for the future energy mix.

Our understanding of climate change has grown rapidly in recent years. The scale and urgency of the threat it poses is of such magnitude we need to have every option at our disposal that can provide us with low-carbon energy. Nuclear is low carbon, even taking into account the energy used to build, fuel and decommission it.

Furthermore, Britain is becoming dependent on foreign supplies of gas and oil at precisely the time when global demand is growing from emerging economies like China and India; and energy supplies are becoming more politicised. Fossil fuels have also become more expensive, and renewables remain stubbornly more expensive than alternatives, and will receive ongoing support through the renewable obligation. If we want stable, lower carbon and lower cost energy, nuclear is potentially an important part of the answer.

So we need to take a decision now. That’s why we’re consulting on the question of whether it’s in the public interest to allow energy companies the option to build new nuclear as part of the answer to climate change and energy security.

The Tories have sought to use the issue of climate change and energy to green-wash away their ‘nasty party’ image. But, like so much of what David Cameron says, look a little closer and nothing much seems to have changed. He has said he likes green energy, but there are Tory councils across the country blocking wind farms – even the largest off-shore wind farm is being blocked by a Tory council. His planning minister called for a ‘moratorium’ on new wind farms. And he doesn’t lift a finger to condemn either.

On nuclear power, he sees the divisions in his party and ducks the question. A new nuclear plant will take about a decade to come online. To say that the Tories won’t build nuclear until the last moment – when it’s too late – has no credibility. People expect governments to take decisions in good time. He clearly can’t. Meanwhile, Labour is confronting these challenges. By 2020, the policies we’ve set out will save from 23 to 33 million tonnes of carbon, the equivalent of taking every car and lorry off the road forever. That’s a good start – but there will be more to do.