Public musical gatherings (apart from Divine Service) would normally require a licence. The key word ins "public". If you let punters in off the street, for payment or otherwise, then the venue must be licensed. The trouble is that standard conditions are often applied which are designed for night clubs and concerts rather than small informa events.

Before Mr Gall jumps in to contradict the major exception is where customers of a public house are singing or playing for their own entertainment rather than to an audience. This should exempt most sessions and in fact most do seem to be quietly ignored but some to get classified as "entertainment" for various reasons which causes a licence to be demanded.