Newly-released intelligence files have revealed how British spymasters used an enticing female agent to test trainee spies during the Second World War.
'Agent Fifi' would haunt the bars of upmarket hotels in wartime England, waiting for the chance to entrap rookie spies.
Elegantly dressed and posing as a French journalist named Marie Collard, she persuaded dozens of would-be agents to spill the beans and reported back to her spymasters.
She was employed by the Special Operations Executive (SOE) - Britain's Second World War sabotage organisation - to test new agents before they were sent behind Nazi lines.
Her official file, released today by the National Archives in Kew, show that she was in fact named Marie Chilver and was the daughter of an English father and a Latvian mother.
She came to the attention of SOE in 1941 after she helped an injured British airman shot down over France escape back to England, having first escaped herself from a prison camp.
She was eventually selected as an "agent provocatrice" with the job of testing trainees at SOE's "finishing school" at Beaulieu.
Her brief was to see if they were capable of maintaining their cover stories without compromising their mission, and all too often she revealed that they were not.
One agent, codenamed Parker, was a case in point. She wrote of him:
Whilst the document's show that she felt some sympathy for the hapless agents, she wrote that her methods were "very mild and innocent" compared with "what is most likely to happen in the field".
"It does give the students a good chance of using their brains (or just their low cunning)," she wrote.
Marie Chilver's file is among 3,300 intelligence and security files from the Second World War being made available for the first time online by the National Archives.