In August 1941, Britain had just signed a friendship pact with the Soviet Union. A "tanks for Russia" drive was about to start.
Yet when MI5 received a tip-off that photographer Lee Miller was a "strong communist" they opened a file on her.
Lee Miller was already something of a celebrity, a glamorous international figure.
American by birth, she had been a model for Vogue in the 1920s before deciding to step behind the camera. After apprenticing herself to the surrealist Man Ray in Paris, she set up on her own, before a brief marriage to an Egyptian diplomat.
But by 1941, she was living with the British artist Roland Penrose in Hampstead. Her son, Tony Penrose, believes it was likely that a jealous colleague went to MI5.
Plus, Lee Miller had also been spotted by Special Branch earlier that summer when she spent a short holiday at the home of Wilfred Macartney in Devon.
Macartney had been jailed in 1927 for trying to sell secrets to the Soviet Union.
He was a well known left-wing figure, the author of a prison memoir.
Special Branch noted that there were five women staying with him in June 1941 - including the wife of Harry Pollitt, leader of the British Communist Party, and Lee Miller.
There is no evidence in the file that Lee Miller ever joined the Communist Party or engaged in any political activity.
MI5 file from the investigation into Lee Millerís "communist sympathies".
Her communism was "more of a mental outlook" officers wrote, and her boss at Vogue, Harry Yoxall "has chaffed her about it".
"She is eccentric and indulges in queer food and queer clothes," he told officers.
Lee Miller became a war photographer, fearlessly following American soldiers as they went into combat.
She was one of the first photographers into the concentration camp at Dachau - that same day visiting Hitler's apartment in Munich.
But still, her MI5 file remained open - and when she returned to London, officers opened her mail.
Once Lee Miller had moved to Farley Farm in Sussex in 1949, with her husband Roland Penrose and young son Tony, the monitoring appears to have eased off.
Lee Miller's own artistic career stalled, but her husband became one of the leading figures in the world of contemporary art.
Then, in 1956, Roland Penrose was appointed to work for the British Council in Paris.
The Foreign Office wanted him vetted.
That enquiry revealed that Special Branch had been keeping an eye on the house and the couple - the file notes that in 1950, Penrose "met the French painter Picasso in Newhaven."
"Information has been received that he is a close friend of Picasso and is engaged in writing his biography".
Aside from Picasso's nationality, the information was accurate.
Although the vetting enquiry concluded that "there would be a risk to security were Roland Penrose to obtain an appointment affording him an opportunity for subversive activity," the couple did go to France.
1956 is where Lee Miller's file ends. But it is obvious from notes on documents that MI5 had another file on Ronald Penrose.
Tony Penrose was surprised to learn MI5 were monitoring his mother.
He says he would very much like to see what they wrote about his father - especially if officers were keeping a close eye on Farley Farm in the mid 1950s.
This was a period when many of the world's most famous artists visited the Farm - Picasso amongst them.
"Many of them had very strong left wing sympathies," he says.
"So I expect whoever was sitting in those bushes was kept quite busy scribbling."
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