A photograph in a Guardian article about Soho photographer John Deakin has been revealed as a picture of artist Francis Bacon in drag. However, there is still a cleavage issue …

A recent Guardian article has led to the discovery of an historic photograph of the painter Francis Bacon – in drag.

The gallery, on the work of notorious Soho photographer John Deakin featured a photograph listed as "Unknown Woman, 1930s". Some might even have concluded that the unknown woman's dour expression and cheap-looking pearls were yet another instance of Deakin's peculiar eye for the sadness of urban life.

But a comment left on the piece led the collection manager of the Deakin Archive, Paul Rousseau, to look again. Commenter bullshotcrummond first noticed that the image had been labelled in a press release as "Transvestite, 1950s" which led another commenter, congokid, to rejoin "Or is it Bacon in drag?"

Rousseau was struck by the similarity straight away. "I'd never considered it before, annoyingly," he says. Searching through the archive, he was able to establish that the photo was one of a set dated 1945 (making them some of the oldest in the Deakin collection), possibly taken for Lilliput magazine, a publication with a reputation for risque photography. There were 15 images in all, and Rousseau immediately set about establishing who the models might be. "I quickly landed on his closest friends Denis Wirth-Miller and Richard (Dickie) Chopping. Denis was a painter and Dickie was semi-famous for designing the original dustjackets for the James Bond books."

"Dickie was known to love dragging up; he was dame every year at the RCA when he became a lecturer there in 1962. And there are many references to Bacon's interest in drag, his wearing of women's knickers and stockings."

Using facial recognition software developed by the CIA, Rousseau produced videos which show that the similarity between Deakin's cross-dressing sitters and these men is, if not conclusive, then certainly startling.

A detail of Francis Bacon, 1952, by John Deakin. Photograph: John Deakin/Vogue

The history of the photographs also seems to suggest that their importance to Deakin went beyond the aesthetic. He kept very little, but for some reason preserved these pictures in particular, later "rescued" from under his bed by the Sunday Times picture editor Bruce Bernard, when he died without leaving a will. The only one of the set which is labelled is Audrey Cruddas, which Rousseau speculates could be because "as a woman, there was no risk of naming her".

If they do show Bacon and friends in drag, Deakin may well have had a more sinister reason for keeping them. Prior to the Sexual Offences Act of 1967, transvestism had been used as evidence in prosecutions against gay men. By never publishing the photos, Deakin may have posthumously undermined his reputation as the nastiest man in Soho.

One question still remains. While the face is very much like Bacon's and the mole on the model's chest closely matches that which can be seen in the famous picture of Bacon holding two sides of meat, it is impossible to ignore the substantial cleavage.

"Deakin was known to fiddle about with photos using basic overpainting techniques," says Rousseau. "Or did Bacon learn to manipulate his 'moobs' like that from his years in Weimar Berlin?"

The origin of the cleavage may be one art mystery that never gets solved.