A senior director at the Nuclear Decommissioning Authority (NDA) has resigned, dealing a fresh blow to the organisation as a report by the Government's spending watchdog confirmed yesterday that the cost of cleaning up Britain's nuclear programme had soared by 18 per cent.

The departure of Mark Leggett, director of the commercial division, was announced to staff on January 18, The Times has learnt. He was responsible for improving commercial performance and boosting sales.

The NDA was established in 2005 to oversee the clean-up of the UK's nuclear sites but it has struggled against rising costs and the departure of key staff. It is looking for a permanent chairman after the departure of Sir Anthony Cleaver last July.

Yesterday, a report by the National Audit Office showed that the estimated future cost of cleaning up the first generation of civil nuclear sites had risen by 18 per cent to £73 billion, compared with estimates two years ago.

Critics say that the NDA has failed to manage the decommisioning programme properly, allowing costs to soar. In 2005, the estimated cost of cleaning up its 19 sites, including Magnox nuclear power stations, research sites and fuel storage and reprocessing facilities at Sellafield, was put at £61 billion.

Richard Bacon, Conservative MP for South Norfolk and a member of the Commons Public Accounts Committee, said that the costs were “spiralling out of control ... The authority needs to reduce the pressure that the work at Sellafield is putting on its operations by cleaning up Sellafield as a matter of priority.”

Key decommisioning programmes at Sellafield, such as the demolition of Calder Hall, the world's first civil nuclear power station, which closed in 2003, have been put on hold because of a lack of funding.

Nathan Argent, of Greenpeace, said that the report demonstrated that building new nuclear plants was “pure recklessness”.

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