Re McGrath's question:

Even one musician playing is illegal without a public entertainment licence if the 'performance' is open to the public. The legal interpretation of the word 'public' can be a bit fuzzy, but a gig in a nursing home, if it were in the reception area, could be counted as public.

The exceptions to this general rule are:

a) if the music is part of a religious service b) on Crown land c) up to two live performers in on-licensed premises (but be warned: any combination of live and 'recorded sound' which includes MIDI, is illegal without a PEL)