Whitehall was desperate to debunk claims that the imprisoned Nazi Rudolf Hess was really an imposter, the files reveal.
By 1979 Hitler’s deputy had been behind bars for almost four decades, after flying to Britain in 1941 on a one-man mission to end the war.
But Dr Hugh Thomas, a former British army surgeon who had examined him in Spandau Prison, claimed the prisoner was a different man - a mistake, he said, that had been covered up.
His theory was dismissed publicly, but we now know that officials quietly commissioned a series of reports demolishing what they considered to be the weakest points in his argument.
Hess was found hanged at the prison in 1987, aged 93. The official verdict of suicide was rejected by his son, who claimed he was murdered.