Change the Law
A proposed solution, involving a small change to UK copyright laws.... (as a copyright holder, I think my proposal is fair.)
If a consumer, or business, purchases copyrighted material then they purchase the right to distribute that material, providing that said distribution does not bring any fiscal/financial profit directly to that consumer.
So, if I buy a CD and play it at a house party for my friends, or at work for colleagues, I have broken no law, but if I hold a ticket-only rave and charge for people to attend, then I owe the artists who made the material a slice of the profit.
Surely this is what PRS is actually trying to achieve? It's not fair to make a profit from someone elses labour without sharing that profit with them (Corporations, take note!), but it is equally unfair to charge someone for listening/sharing music they've already paid for!
The rules regarding the copying and illegal distribution of material should remain unchanged. If you want to enjoy copyright material at your leisure, you should pay for it, but it shouldn't be a crime to share that with others providing you don't give them their own copy or charge them for the experience of doing so.
Indeed, I think that such an egalatarian approach might actually increase the sales of copyright material as more people are exposed to it. Closing down the avenue of 'passive advertising through exposure to product' is surely not good for business?