Paul B: to join PRS you have to be a songwriter or publisher. The small clubs and gigs scheme allows them to report their own performances. The debate is whether/how people who are not songwriters but who simply perform other people's songs in environments which are unlikely to get reported by the PRS licence holder or sampled can report them, so the royalties get to the right people.

It's not free, but the £10 is deducted from royalties. I suspect if I were to join on the basis that I've written a handful of tunes then the PRS would wait quite some time to recoup this :). However when I looked into it before I'm sure I read that by joining you assign all control over your compositions to PRS to administer, and I'm not sure I want to do that.