Hurricane photo by Aeroplane magazine/www.aeroplanemonthly.com
Two amateur historians have uncovered the story of an audacious spy, who infiltrated the RAF in the middle of World War II and escaped back to Germany in a stolen RAF Hurricane.
Augustin Preucil came to Britain along with scores of other Czech pilots when mainland Europe fell under Nazi domination.
The first clue to Preucil's treachery came when Richard Chapman, an historic aircraft enthusiast who lives in Germany, came across some old photos from the German National Aviation Museum in Berlin.
Dating from 1941, they showed an RAF Hurricane on display among German aircraft.
The squadron markings were clearly visible and Mr Chapman, intrigued to know how the Hurricane got there, set about tracing the aircraft.
Mr Chapman enlisted the support of Roy Nesbit, an air historian with 20 books to his name, and who had himself served in the wartime RAF.
He went from one unit to another and must have gathered a lot of information about RAF morale and, of course, its shortcomings
Together they established that the plane belonged to "55 OCU" - an Operation Conversion Unit which trained foreign pilots converting to British aircraft.
What's more they found an official loss report relating to the plane in the picture; it said that the plane, and its pilot Augustin Preucil, had been lost, presumed crashed, in the North Sea off Sunderland.
Preucil had taken off with another pilot, a young Pole, to practice dogfights over the sea.
The Pole returned to base reporting he had seen Preucil in a steep dive and assumed he had crashed.
In fact Preucil had flown his machine across the North Sea to Belgium.
There he landed on a farm and was offered food and shelter by the farmer and his family .
But Preucil immediately betrayed them to the Gestapo and the family were imprisoned.
Preucil went on to work for the Gestapo mainly by infiltrating Czech political prisoner groups in concentration camps; it is known that some of those he betrayed were shot.
When Germany was finally defeated Preucil was captured by the Czechs and put on trial for treason.
He was executed in 1947.
So how was it that Preucil was able to be accepted by the RAF and remain undiscovered?
Pictures were uncovered at the German National Aviation Museum. Photos by Aeroplane magazine/www.aeroplanemonthly.com
Roy Nesbit says that in the early 1940s Britain welcomed many pilots from Poland, Czechoslovakia, Greece, Holland and France whose countries had fallen to the Nazis.
"They were very valuable to us" he said.
"The Czechs, especially were courageous. We had a very high regard for them.
"They had a fervent feeling to fight the war, often they were more ferocious than we were. But Preucil was an exception. He was a complete traitor."
Mr Nesbit says that the pilots wouldn't have been very carefully screened and it would have been easy for Preucil to dupe the British authorities.
Mr Chapman believes that Preucil would have had a lot of information of use to the Germans.
"He went from one unit to another and must have gathered a lot of information about RAF morale and, of course, its shortcomings."
Mr Chapman says that in his experience the Preucil story is unique.
"This is the first time I've heard about an agent in the RAF" he said.
The Preucil story leaves many questions unanswered, the most important being who was his handler?
Roy Nesbit thinks he must have been working for a German controller here in Britain.
But so far there are no clues as to the handler's identity and Mr Nesbit believes the files that would reveal it are still classified as secret by the government.