Some of the music is traditional - no one knows
who wrote it and it's been around for centuries. There's also
quite a lot written in the old style by known composers and the
production of new music for dancing seems likely to continue. Some
of the music isn't even English in origin and sources include
other parts of Western Europe and the Americas. Some has been
derived from Morris tunes probably because some of the musicians
play for that too.
The Morris influence may be whyMelodeonsfeature in many of the bands but almost any instrument is "allowed". Here's a short list of instruments: fiddle, recorder, whistle, saxophone, percussion, clarinet, mandolin, guitar, keyboard, dulcimer ... Over the last 40 years, cheap and effective electronics has made it possible to accommodate almost any instrument.
This unusually large band put together for a special occasion shows a variety of instruments
The following band websites have links to sound samples:
A more extensive listing is here and these "search links" that will probably find more for you: