As far as I know they don't.
PRS is not the only option in UK, we can sign up with BMI but they said to me that if my main performances are in UK or going to be in UK and if I'm myself based in UK it will make more sense to register with PRS.
Nadia
http://iacmusic.com/artist.aspx?id=137230
http://www.soundclick.com/bands/default.cfm?bandID=936270
http://www.songramp.com/homepage.php?userid=27495
http://www.showcaseyourmusic.com/nlcripps