DAVID Cameron is being urged to come clean on plans to transport dangerous nuclear materials that could be used for nuclear weapons from Scotland to the United States.

The SNP said the UK Government must provide “full transparency” on its plans after US documentation showed the transfer was in the interests of “US national security”.

It comes days after Cameron told a nuclear security summit in Washington that 700kg (1,540lbs) of highly enriched uranium (HEU) would be transported to the US from the Dounreay storage facility in Caithness – the site’s largest ever shipment.

According to a 2015 document written by the chief of the Special Fuel Licensing Branch in the US Government’s Office of Nuclear Material Safety and Safeguards, authorisation had been granted under an extended Certificate of Compliance to transfer five special fuel assemblies of uranium with special conditions.

The certificate noted that the shipment of these assemblies, containing numerous rods of highly dangerous uranium with cooling periods of several decades, was in the “interest of US national security”.

It was originally issued in 2012 but has been extended on three separate occasions, writes the US government’s chief of Special Fuel Licensing, to allow transfer of the uranium before December 31, 2016.

Dr Paul Monaghan, MP for Caithness, Sutherland and Easter Ross which includes the Dounreay site, said the Prime Minister had to come clean.

He told The National: “Just last week we learned he had authorised the largest ever shipment of highly enriched uranium from Dounreay to the United States, and we know this is going to the Savannah River site in the United States, which was built to refine nuclear materials for deployment in nuclear weapons.

“Of particular concern is the elevated level of importance attached to this shipment by the United States government. Indeed, the Certificate of Compliance clearly states that the shipment is in the interest of US national security.

“This is a deeply worrying development and we have to ask ourselves why the United States government recognises these special fuel assemblies as a national security issue, who actually owns this material, why it is that the UK Government appears to have been stalling this particular shipment of what is very specialised structures of uranium, and of course why, perhaps more generally, highly dangerous nuclear material that is considered to be in the interest of US national security is being held at a civil nuclear site in Scotland.”

Monaghan said the US government would not extend such certificates without careful consideration and planning.

“This particular certificate has been signed by a senior US government official and appears to suggest that the UK Government has either been refusing to transfer these special fuel assemblies of uranium or has been unable to transfer the highly dangerous nuclear material for some other reason,” he said.

“This disclosure implies that the UK Government appears to have been conducting international aspects of the vitally important business of nuclear decommissioning in an unacceptably ad hoc manner, just at a time when David Cameron has been announcing plans to transfer massive amounts of highly enriched uranium from what is, crucially, a civil nuclear site in Scotland.”

He added that the people of Scotland had a right to know what the UK Government was actually doing at Dounreay, what is stored there and why Cameron appeared not to be operating with the level of transparency people had a right to expect.

Monaghan added: “The fact is that these materials are out of bounds for military use under the Euratom safeguards convention, so any diversion for military use would be illegal under international law… Any agreement between the UK and US requires Euratom concurrence and it would therefore be illegal to transfer material for non-peaceful purposes.

“Everyone appreciates the need for secrecy when it comes to handling nuclear materials, particularly at this time of heightened threat, but the UK Government must now explain why vast amounts of uranium and other nuclear materials considered so dangerous as to be of national security interest to the world’s most powerful nation are being held in Scotland at a civil nuclear site.”

A DECC Spokesperson commented: “The UK has robust nuclear safety and security arrangements. The recently announced swap will deliver real societal benefits – both in the UK and across Europe. We can’t go into detail regarding the movements of nuclear material for security reasons.”