The £73 billion cost of decommissioning nuclear power sites could be increased "significantly", the head of an influential committee of MPs have warned.
Edward Leigh, chairman of the Public Accounts Committee said the cost of work over the next five years had already risen "steeply."
The committee said in a report that the Government was unable to provide a complete assurance that the cost of decommissioning new nuclear power stations would not fall back on future taxpayers.
The MPs recommended that before giving the go-ahead to new nuclear power stations, the Business Department should ensure that operators can meet future decommissioning costs.
The report said: "Uncertainty around costs far into the future is understandable, but uncertainty over the escalating costs of work due to be carried out imminently is difficult to justify."
Mr Leigh said: "Decommissioning the UK's first generation of civil nuclear sites and running the remaining sites still operating will cost an enormous amount of money. The latest estimate, prepared last year, puts the cost at £73 billion over the coming decades.
"We cannot be confident, however, that even this figure will not be significantly upped when the estimates are next revised. Estimating costs far into the future is of course a precarious business, but elements of cost that might be expected to be more predictable - such as for work expected to be undertaken over the next five years - have risen steeply.
"An important lesson is that, when new nuclear facilities are built, plans for decommissioning them should be already in place. The Department is unable to provide complete assurance that the costs of decommissioning new nuclear power stations will not fall back on future taxpayers."
Robin Oakley, head of Greenpeace's climate and energy campaign, said: "More nuclear power stations will hit the taxpayer in the wallet. It's already costing the UK public billions of pounds to decommission and clean-up existing nuclear plants, and the misguided Government push for more nuclear power stations will sting taxpayers for billions more.
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"Worryingly, this report points out that the Nuclear Decommissioning Authority is years away from pinning down an estimate of how much it will cost to deal with the nuclear waste that we're already burdened with; it already stands at £73 billion, and it's highly likely that it will pass the £100 billion mark... Anyone - including Gordon Brown - who wants more nuclear power stations is either economically incompetent or doesn't give a fig about the UK taxpayer."
