FOR AT least two years, Britons nervously watched the seas and skies of the English Channel for a Nazi invasion fleet that never came.
But remarkable, newly-released British secret service documents reveal that Hitler planned an invasion of an entirely different kind from the extreme north of Scotland.
Instead of ships, troops and tanks, the Nazi dictator wanted to introduce lethal bacteria to Shetland, from where they would spread death and panic across the British Isles.
The declassified documents show the amazing plot began in January 1943 when three exhausted Norwegians staggered ashore in Lerwick after a 46-hour journey across the North Sea from Nazi-occupied Norway.
Because the registration number of their fishing boat resembled that of a missing Special Operations Executive (SOE) vessel, the men received a VIP welcome. The boat was not searched and the men were taken south without having to answer any awkward questions.
Alarm bells rang shortly afterwards, however, when MI5 intercepted a German signal saying the boat, the Reidar, had left Norway on a mission for German intelligence.
The men were detained and immediately transferred to the Camp 020 interrogation centre - a Victorian mansion surrounded by barbed wire on Ham Common, London, run by Colonel Robin Stephens, known as 'Tin Eye' because he wore a monocle. It was there that the bacteria plot began to unravel.
Investigators established the Germans were attempting to copy the famous 'Shetland Bus' - the popular name for the escape and supply route between occupied Norway and Shetland, run by the SOE using fishing boats.
The extent of the threat began to emerge as the inquiry discovered no fewer than 50 fishing boats had been assembled by the Abwehr Stelle, the German intelligence office in Norway.
MI5 focused their attention on one of the three crew from the Reidar: radio operator Arnold Evensen, 28, who turned out to be a member of German military intelligence and carried the cover name Alex. Agents decided the skipper and engineer were innocent, following a common German practice of placing one agent among a group of genuine refugees.
The documents show Evensen talked willingly. He revealed Captain Lieutenant Klein, the new head of German intelligence in Trondheim, Norway, had ordered the Reidar to be sent to Shetland as a "feeler".
To their horror, MI5 then discovered that if the Reidar trip succeeded, spies and collaborators would be sent on subsequent journeys "and these would also be equipped with the necessary material for spreading bacteria in this country".
Camp 020's record of Evensen's statement shows that one method for spreading bacterial culture was to hide it inside pens and pencils.
Another newly-declassified report says Evensen never learned more about the biological warfare threat, but that another agent in Norway "appeared to be most anxious that the British should be warned about this".
Evensen said that Klein had told him the German plan was for him to agree to be enlisted by the British and sent back to Norway with a radio transmitter, so the Germans could send false information.
Evensen continued to maintain that he was, in fact, a loyal Norwegian who had joined German intelligence to support the Allied cause.
He proposed that he should return to Norway with two transmitters, using the second one to send genuine information to the British without the knowledge of the German spymasters.
He suggested the BBC should broadcast the sentence "There is a land with eternal snow" in Norwegian at two specific times, so that other members of the resistance group would know that the mission had been successful.
So convincing was Evensen, and so impenetrable his story, that MI5 remained baffled as to which side he was really on. Their lengthy interrogations of him fill most of four thick files on the Reidar case, which are among over 300 secret intelligence files released by the National Archives today.
The Germans were eager to use Lerwick for their own 'Shetland Bus', Evensen said. German agents had been placed in Lerwick, and local knowledge was also being provided by a Dutchman with the cover name Furu, who ran an undercover operation for the Germans and who had travelled to Lerwick from Norway up to eight times.
Evensen said Klein told him that because of earlier botched attempts, he would be shot if he failed this time, but that if he succeeded he would get "a large reward and a big job".
But MI5 harboured serious doubts about Evensen's claim that he belonged to an ad hoc Norwegian underground movement and never seriously considered sending him back to Norway.
One intelligence officer, Major Munthe, wrote that Evensen "gave me a strong impression of being an abnormal potential criminal idiot - almost certainly sent here by the enemy".
A Captain Shanks at Camp 020 concluded that "his mental powers are abnormal, his memory hopeless and his mind an inchoate jumble".
But if this were the case, how had Evensen been taught so quickly by the Germans to become the skilled wireless operator he certainly was?
One British official thought that his "dullness and bad memory" were "a defensive mechanism".
Lt Col AP Rawlinson of MI19 wrote that "there is strong reason to believe that the gentleman is in fact endeavouring to put across an ingenuous triple cross on one of our secret organisations working in Norway, and that he is to all intents and purposes a genuine enemy agent".
At one point, an exasperated British official wrote: "He is either mentally subnormal or more cunning than he appears to be - possibly both."
The British finally concluded that Evensen's story was probably true, and that in any case, by mid-1944 he was no longer a risk.
He was released on condition that he should never be allowed contact, or fall into the hands of the Germans again.