THE pre-war suspicious activities of 50-year-old Dundee hairdresser Jessie Jordan led J. Edgar Hoover's G-men to smash a major German spy ring in the United States, the newly released MI5 papers reveal, writes writes James McKillop.

A plot involving decoying a senior American staff officer to a New York hotel where he would be overpowered and forced to reveal secrets of American Atlantic coast defence operations was directly linked to Jordan. MI5 foiled the plot because they were intercepting her mail.

A German agent based in the US and codenamed Gold had described the plot in a letter to Jordan for forwarding to Germany.

MI5 were astounded that no attempt was made to encode the message. They immediately informed the American authorities and a major Nazi spy ring in the United States, involving up to18 agents, was smashed.

Jordan was being used as a post box by the German secret service to forward mail from agents in various parts of the world, including the spy ring in the United States, to Hamburg.

However, as MI5 investigations progressed they found that she was also actively involved in direct espionage. She visited military sites in Scotland and the North of England and filed reports to Germany.

To all intents and purposes Jessie Jordan was a rather nondescript person. However, with Scotland on war alert - even as early as 1937 - suspicions were being reported to the authorities.

Various visits made by her to Germany were also being monitored. Such was the suspicion surrounding Jordan that an employee went through her handbag and found a map of Scotland and Northern England with key military installations marked in pencil.

Born in Glasgow, the illegitimate daughter of a Coatbridge servant, Jessie Jordan married a German and spent her happiest years in Germany.

She claimed that on her return to Scotland she had been ordered to spy for Germany. ''I have no passion for any country,'' she said on being sentenced to four years penal servitude. ''The sentence is my medicine and I can take it.''

q The mystery of whether a Dutch double agent codenamed King Kong gave away the secret of the 1944 Arnhem landings to the Germans appears unlikely to ever be solved, after a mass of official records released yesterday failed to give a conclusive answer.

The spy, Christian Lindemans, given his nickname in recognition of his physical bulk, was vilified after the war for betraying the Allies and contributing to the losses they suffered during the airborne assault.

Operation Market Garden, the attack centred on Arnhem, was a major reverse for the Allies.

Files about the case, released yesterday by MI5 to the Public Records Office in London, do indicate Lindemans gave German forces some sort of a warning.

Two German soldiers who dealt with the Dutchman recalled being told Lindemans had given warnings of an airborne attack on the night of the Arnhem landings. However they said he had identified the attack site as Eindhoven, 30 miles away.

After his arrest, Lindemans committed suicide in jail in 1946.