The name of the researcher is David O’Keefe, and when he confronted British Naval authorities with his evidence, they acknowledged that he had discovered the truth.
Though not a major port, there was a naval HQ based at Dieppe, specifically at Hotel Moderne. There was also an important radar installation located in this area. Intelligence was certain that trawlers based at the harbour were also being used as spy ships. The special commando unit was instructed to search both the hotel and specific boats in harbour.
Of course, if the enigma machine was to be found (the 4-rotor type), gleefully running off with it tucked under your arm and thinking the Germans would be none the wiser - I'm sure allied intelligence was aware of this and had no intention of removing it.
Again, the only thing that hasn't been proven is this 'spy mission' was the major driving force behind the Dieppe raid.
regards,
Jack