MPs have called for a full statement in Parliament after Sellafield, Britain's major nuclear site, confirmed it had "lost" 30 kilograms of plutonium.

An annual check of nuclear material at all of Britain’s civil nuclear installations published today showed that 29.6kg of the radioactive material was unaccounted for in the last financial year at the Sellafield site in Cumbria.

The loss, first revealed in The Times, has been explained as an auditing issue rather than plutonium actually going missing.

But Andrew Mackinlay, Labour MP for Thurrock, believed Parliament should be given more details. "I don’t think this is good enough. I think there needs to be a full statement to Parliament about this business if the public are to be reassured," he said.

Norman Baker, Liberal Democrat environment spokesman, said: "If the figures are wrong then this looks like serious incompetence from an industry that deals with highly dangerous resources.

"Those who argue for a new generation of nuclear power stations ought to reflect on the inability of the industry to ensure the security of the power stations it has already got."

Eddie McGrady, an SDLP MP from Northern Ireland, has demanded an investigation into the way nuclear material is accounted for. "This recent error raises serious concerns about the accounting mechanisms that are in place at Sellafield," the South Down MP said.

Jean McSorley, a Greenpeace nuclear campaigner, said the missing material was enough to make four nuclear weapons or a large number of "dirty bombs".

"What the nuclear industry needs to do is stop reprocessing spent nuclear fuel, a process which releases weapons usable plutonium. Instead they shouldtreat spent nuclear fuel as waste and keep the plutonium in the fuel, so it can’t be stolen and made into weapons," she said.

The British Nuclear Group (BNG), which operates Sellafield, denied that any material had disappeared. "This is material that is unaccounted for, and there is always a discrepancy between the physical inventory and the book inventory," a spokesman said. "There is no suggestion that any material has left the site."

The discrepancy compares with a 19kg loss at Sellafield in 2003 and a cumulative loss of about 50kg at the Cumbrian plant over the past ten years. "Some years there is an apparent gain, some years there is an apparent loss," the BNG spokesman said.

The UK Atomic Energy Agency said that in most cases, unaccounted material resulted from uncertainties in the measurement systems used to produce the basic data and did not indicate real gains or losses of nuclear material.

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