I used to go to raves all the time in my 20s and early 30s in London. I can't say I saw anything to untoward myself, but certainly heard some stories. Although the music I went to wasn't so mainstream, it was a lot harder drum and bass and Dutch hardcore, where you'd generally get a lot nicer crowds and tend to see the same faces.I think perhaps in the UK it is not all that rare for young women to go out to raves / nightclubs / pubs, go back to a mans house and be given more drink / drugs until passed out and then the man or several men takes advantage of the situation.
There were certainly many known cases local to me of that happening and I am in a very low population and low crime area supposedly.
There must be loads of cases going on in Cities like London and Manchester on the weekend.
One of my friends that is female told me once, she used to get groped all the time walking through crowds at clubs and it was just normal to her and didn't really bother her too much. That did really **** me off because doing something like that wouldn't even cross my mind, so just goes to show how quite a lot of men will take advantage if they can. I imagine that is a path that leads to other things fairly quickly when alcohol/drugs is involved for some rotters.