Mr Brennan said: ‘Two weeks ago, I asked the Lord Chancellor's Department to release all of those official documents relating to the Abdication that are still closed to the public. I was told that, in the light of the death of the Queen Mother, a re-review of those papers was going to be undertaken before the end of the year.

‘The latest revelations concerning the Duke and Duchess of Windsor, and President Roosevelt's worries about their links with the Nazis, gives added urgency to the need to release all remaining state papers dealing with both the abdication and the British Government's attitude towards the former King and his American wife.

‘It is totally unacceptable that British people have to rely on overseas sources to find out about their own history,' said Mr Brennan.

‘The public deserves to know whether or not the Government of the day held similar suspicions of the Duchess's political beliefs and whether, like the FBI believed, this was a major factor in the abdication of Edward VIII.

‘The reasons behind the abdication, and the roles played by various members of the Royal Family are matters of historical importance. Not only do we not know what part the Queen Mother played in this melodrama, but now we have foreign intelligence reports that suggest that the Duchess of Windsor may have been passing secrets to a Nazi lover.'