A British energy adviser says Tony Blair's plan to stop building nuclear power stations in order to concentrate on renewable energy is flawed.
Ian Fells says the nuclear industry must not be reduced
The prime minister said Britain would agree a goal of a 60% reduction in carbon dioxide emissions by 2050.
But Professor Ian Fells, of Newcastle University, a science adviser to the World Energy Council, said there were concerns about the long-term impact of this policy.
He told BBC News: "It's a laudable effort to try to go to a low-carbon economy, but the kind of strategy that's outlined is a bit worrying.
"There is an enormous emphasis on renewables, which I agree with, but it's going to be very difficult to do in any engineering terms.
I'm sorry to say I think it's rather a reckless policy
"In fact, from an engineering point of view, it's thought a 10% renewable energy target might conceivably be reached, but it won't be reached by 2010.
"To talk about 20% or higher aspirational numbers means an enormous influx of capital and engineering effort."
Professor Fells said his biggest worry was that the emphasis on renewable input was at the expense of the nuclear industry.
"But if you run the nuclear industry down, you have to replace it with something, probably gas, according to Patricia Hewitt speaking this morning.
"If you do that, what happens is you increase carbon dioxide emissions, so your environmental aspirations would actually be in tatters."
He said in 20 years' time, the UK would be importing 90% of its gas.
"And relying on most of it coming from Iran, Russia, Norway to an extent, so your security of supply is also jeopardised.
"So I'm sorry to say I think it's rather a reckless policy."
The professor warned the White Paper could have serious consequences for other environmental goals.
"The problem with global warming is a very serious one, one of the most serious problems that we face, and we're working hard towards it.
"But frankly, if we decide to throw away our nuclear input, then the situation is such that we have no chance of achieving it."