[djfierce]

well, you as the songwriter should be a member too, the minute you put a song out there commercially, you should be a member, this also covers airplay, you get paid for the average amount of times your song is played.
Yes you can do something if i perform it, you report me to the prs and they sue my arse and pass on the relevant fees and whatever comp is awarded to you, legal cover is a big reason why alot of artists are members, otherwise it's the lengthy and costly procedure of pursuing me on your own 'dime' which you may or may not figure is worth the hassle.
But if you werent a member then it's difficult for you to do so because as long as i have performed with a license or in a venue with a license then i can claim i have done everything i am required to do by the ruling music commision, which in the uk is the BPS who polices this part of the industry via the PRS, they make sure anyone playing or performing music pubicly is licenced to do so, usually spot checking places