What would females in Britain say? Their mates?
We don't really have a way of differentiating between the genders when talking about mere friends.
I met a friend for lunch yesterday.
Oooooh, really? Male or female?
Oh, one of the girls. It was Jane.
I met a friend for lunch yesterday.
Really? Who?
John.
We are starting to hear "girlfriend" used to refer to a female friend but I think the vast majority of Brits would still assume that a female referring to her "girlfriend" would be a lesbian and therefore referring to her female romantic partner. If she said "I met
a girlfriend for lunch yesterday" we would be less likely to assume she was a lesbian but the word would still sound slightly unnatural.
With the usual double standards that exist in language, I don't think either AmE or BrE allows for a male to say "my/a boyfriend" without a clear suggestion that he is gay and therefore referring to a male romantic partner.