Thanks everyone for all the info on this. I hadn't realised how complex the issue was.
As regards the landlady DtG, the pub in this case is one of those dying breed of small owned village pubs that struggles to survive. We do like playing in these type of pubs - and for our own enjoyment - as clearly they are glad of our custom, but understandably they are not keen to have yet another fee whacked onto them. At the time she was really worried about 'doing something wrong' so rather than create any trouble we moved elsewhere.
I may well follow up your suggestion Leadfingers, as I am fairly confident that most of the tunes we end up playing are "Trad" or "Anon". Mind you I may well have a bit of difficulty, because often when I am asked what tunes I have just played, I am hopeless at remembering the names of them!
Playing the radio for customer benefit does sound like a bit of a double whammy to me, surely the PRS claims a hansome fee from the radio station for broadcasting the music - and rightly so - but it seems a bit rich to then charge whoever actually turns a radio on to listen to it.
Sally