BBC News 24 investigates Dounreay's missing uranium

One nuclear expert said the material could be enough to make a dozen atomic bombs.

The Scottish Nationalists demanded an immediate inquiry to find out what had happened to the uranium.

The worst case scenario being presented is that the material could have been taken for a nuclear arms programme.

'We are not being told the whole story' - SNP

BBC reporter Eleanor Bradford in Glasgow: "Environmentalists say there is a danger to the public"

The uranium went missing between 1965 and 1968, according to a report by the UK Atomic Energy Authority.

The extent of the loss was discovered during a study of one of the plant's waste shafts, which had been used as a dump.

The SNP's environment spokeswoman Roseanna Cunningham said a commission should be established to uncover the truth about the latest in a series of embarrassing episodes at the Dounreay plant in Caithness, in northern Scotland.

"How on earth can material as deadly as this just go missing?" she said.

"As usual one gets the feeling that we are not being told the whole story.

"Either that or Dounreay's incompetence down the years has been even worse than anyone imagined.

"We have been fighting for a general inquiry into Dounreay for some time, but now it is clear we need a truth commission where all the workers, past and present, are exempted from the Official Secrets Act. Only by doing this can we ever hope to get to the bottom of Dounreay's history.

"We are now in the ludicrous situation where we are hoping that the uranium was used to make British atom bombs because the alternatives are even harder to stomach."

'Worst-case estimate'

Dounreay said the estimate of 170kg of missing uranium made in a recently-published inventory was "a worst-case estimate" of the content of the waste shaft.

The uncertainty arose because Dounreay processed material from a range of sources in the 1960s, a spokesman said.

Inquiries in both 1963 and 1973 concluded the missing material was probably due to uncertainty in estimates of the uranium brought to the plant.

"This reflected the imprecision of the analytical techniques available at that time, coupled with the difficult nature of the input material," the spokesman added.

String of embarrassments

The clean-up operation on the shaft began at the end of March, when the government confirmed it was leaking radioactivity. The work is expected to take 25 years.

Then in April the government announced it was taking 5kg of uranium from the former Soviet republic of Georgia to prevent it from falling into the wrong hands.

This prompted criticism from Scottish Nationalists and environmentalists.

The attacks increased when on May 16, the Health and Safety Executive revealed a sweeping safety review of the Dounreay plant.

The inquiry followed an incident when a digger cut through electrical cables, paralysing the plant after the emergency supply also failed, prompting concerns about the control of the plant.

Ms Cunningham added: "The waste shaft at Dounreay - the ultimate cover-up - has been a disaster story in itself and now we find more problems lurking inside.

"Whether this latest development reveals deception or simply yet more bungling inefficiency, the consequences are a confusion which is potentially dangerous.