At around the 47 minute mark of Forbidden Love: The Unashamed Stories of Lesbian Lives, one of the women interviewed, Carol Ritchie-MacKintosh, talks about the persecution of gay men in the mid-20th century:
CRM: Well, at that time, it was illegal to have a house party with only one sex. So you at least had to have two women. Now, you could have 45 men and two women. And as long as the women were discreet and could sit in the library, and let the boys do what they liked, and simply answer the door, there was no problem.
Interviewer: What happened if there weren't women there?
CRM: They would raid it. They would absolutely raid it. They would level it, the police.
I was curious about this and tried to do some internet research on Canadian law during this period but did not find anything. This also reminded me of an oft-circulated myth about laws restricting the number of unrelated women living together, on the premise that a residence with too many such women would constitute a brothel, which made me suspicious.
I believe what is being said here, but was there actually such a law, and if so, could a reference be provided for it? I can imagine that the police might want to raid a single-sex party if they suspected that it was really a gathering for homosexuals, but that is different from saying that all single-sex house parties were unequivocally illegal. (Moreover, I would think that very traditionally-minded people might have accepted or even preferred single-sex parties, for the same reasons for which they might have been supportive of sex-segregated in social or educational settings.)