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Labour has demanded an investigation into “cover-up” claims that key Government files vanished after being borrowed from the National Archives.

Whitehall departments have “lost” almost a thousand documents detailing controversial episodes around major events including the Falklands War, the Troubles in Northern Ireland and tests on polio vaccines after loaning them from the records bureau, the Guardian reported.

The disappearances raised fears over how government ministries can remove official papers long after they have been declassified and made available to the public.

A National Archives spokesman said: “The National Archives regularly sends lists to Government departments of files that they have out on loan.

“If we are notified that a file is missing, we do ask what actions have been done and what action is being taken to find the file.”

Shadow Cabinet Office Minister Jon Trickett said: "The ‘loss’ of documents about controversial periods in history is unacceptable.

"The British people deserve to know what the Government has done in their name and their loss will only fuel accusations of a cover up.

"These important historical documents may be a great loss to history – and their disappearance must urgently be investigated.”