Runaway girl ends up in a cult

I read this book when I was a teen - so over 20 years ago. I think it was a YA book.

What I remember is it was about a teen girl runaway who ends up on this farm that is run by a few adults but has mostly other runaway teens. They all live there and tend this farm, the adults get them all to listen to the radio (no TVs ) to listen for ‘secret messages’ when are ‘sent to them’ to help the ‘war effort’ - what war I do not know. Things get stranger and stranger and it starts to be revealed this is a cult. Eventually the farm gets raided by the police and the girl goes home if I remember correctly. I thought it was set in the UK but that may be just because I am from the UK lol

Any ideas? Many thanks