I know I'm being dull again, but the distinction between composer and performer has always caused grief. Plenty of household names get absolutely nothing from PRS, because they only performed the songs, they didn't write them. Back in the 60s, it was rare for the performers to write the songs, and quite normal to simply get offered them. If anybody remembers those awful sound-a-like records we had in the 70s, where there was a little note that said "features none of the original musicians" - this was simply a way around PPL. The composer got their money, but as it was recorded in the studio my un-named musicians who simply got a days pay, the costs were much cheaper. Barry Manilow was a prolific song writer, as were Lennon & McCartney, so everytime somebody covers one of their songs, the till chinks. If you scrutinise the small print on songs by people like the Spice Girls, you see they have a co-writing credit, so they get a percentage of the songwriters income. I guess giving away some of your rights is better than having 100% of nothing!
There are actually 3 copyright agencies. PRS, PPL and MCPS (the mechanical copyright protection society) - Two went together into the PRS-MCPS Alliance, but now this is called PRS for Music. The mechanical bit is about the copyright in the physical product - the CD, record, DVD - the 'thing' the protected item is actually on. Copying the CD into a computer system, or onto a compilation CD or onto any other medium, like USB sticks, strictly speaking is a controlled right, and if you do it - you need to pay. It isn't just domestic or business people who can get this wrong. If you use i-tunes, have a read of the agreement and you'll see there are quite specific rules on what you can do and what you can't.
I do actually feel sorry for the hairdresser - PRS are quite high profile with their advertising campaigns, so most people have at least heard of them, but PPL sounds so similar, you can't blame people for not knowing they need multiple licenses. In this case, I suspect when he found out, he decided to not pay on principle, and this is what led to the action. The trouble is that the very best you can do is have your voice heard in court. I'd guess that legal council would advise you to plead guilty, because no matter the circumstances, you did do it. Obviously people consider it unfair, but that doesn't really count in law. It's rather like speeding in your car. If you did it, then you cannot plead not guilty -all you can do is mitigate.