I'm female and just finished A level maths and chemistry, I enjoy them both and am good at them so that's why I took them, however in my classes there were way more boys than girls and the girls that there were during AS dropped them for A2, in part because the boys in the maths class were quite intimidating, and there was a sense that we weren't welcome!
The teachers were very encouraging though, I think it was just unfortunate that a particular group of boys made people feel unwelcome. In my experience at 2 grammar schools I've found that girls generally have a high interest in maths and science, in some years (like this year's y12) there are more girls doing STEM subjects than boys. Maybe because there is an overall opinion that academic subjects are best, so few girls feel obliged to pick arty subjects when they'd prefer academic ones, which might be different at other, less academically-focused schools.