Noreen, the question about local authority licensing was answered in the third post. Nevertheless PRS is also an issue, although it is primarily the responsibility of the venue, rather than musicians and session organisers. However if you want a session to run successfully you won't want to get the publican into trouble, so it helps to understand the rules. As I pointed out, it may not be as simple as assuming that traditional means non-copyright.

PPL and PRS licence different things. PRS manages the composer's copyright. PPL manages the musicians' and record producer's copyrights. To complicate things further, the record producer pays a fee to a third organisation, MCPS, for the composer's royalties when their work is recorded. It's all a bit of a minefield! At least in the UK the organisations work together, in the US they appear to have several different organisations competing with each other.

Fortunately from a musician's point of view, it's not usually your problem.