The lights could go out when coal and nuclear power stations are phased out
The government's new energy adviser says the UK could face blackouts by 2016 because green energy is not coming on stream fast enough.
Ministers have previously denied that the UK is heading for an energy gap.
But David MacKay, who takes up his post at the Department of Energy on 1 October, says that the public keep objecting to energy projects.
This, he says, is creating a huge problem, which could turn out the lights.
Professor MacKay is a researcher at Cambridge University.
His recent book, Sustainable Energy - Without The Hot Air, won applause for its examination of current government plans to keep the lights on whilst also cutting carbon emissions.
It concluded that policy is moving in the right direction, but the sums on energy provision simply do not add up - not enough power capacity is being built.
Speaking unofficially, he told BBC News that this meant that Britain could face blackouts in 2016 - when coal and nuclear stations are phased out.
Professor David MacKay: "The scale of building required is absolutely enormous"
"There is a worry that in 2016 there might not be enough electricity. My guess is that what the market might do is fix that problem by making more gas power stations, which isn't the direction we want to be going in," he said.
"So we really should be upping the build rate of the alternatives as soon as possible."
Professor MacKay blamed the public for opposing wind farms, nuclear power, and energy imports, whilst demanding an unchanged lifestyle.
You cannot oppose them all, he said, and hope to have a viable policy on energy and climate change.
"We've got to stop saying no to these things and understand that we do have a serious building project on our hands," he said.
Professor MacKay said he looked forward to engaging the public in a more open debate about what he calls the realities of energy policy when he takes up his post.
His says his new masters in Department of Energy and Climate Change have impressive commitment to solve the issues.
Professor MacKay's many supporters will hope that he is allowed to continue speaking openly to the public after he takes office.
The Conservatives blamed the government for complacency over energy security. They say ministers have dithered over energy policy.
But Andrew Warren of the Association for Conservation of Energy said the real culprit was the EU.
"The true culprit - if there is one - is rather less public opinion, and rather more the 27 EU governments who insisted on handing out far too many permits under the first and second phase EU emission trading schemes.
"Coupled with a decline in output from heavy industry, this has led to their dumping a vast number of surplus permits onto the carbon market, deflating the carbon price, and thus rendering non-fossil fuel investments far less financially attractive for electricity generators."
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