Hi Mark
Chippenham is usually pretty light as far as melodeon workshop are concerned - it really is a dancers festival primarily. However there are great sessions (at pretty much all hours) and some good mixed-instrument stuff. For the latter I'd particularly recommend
Valmai Goodyear and Bryan Creer's morning tune sessions where they play through and lead 3-5 tunes per day and provide dots to take away or download.
I did hear talk of a playing for morris workshop this year (Simon Care?) but maybe I dreamt it and maybe not your thing anyway. Either way the place will be crammed with box players and there's a good chance of tunes night and day - some organised sessions which will be in the programme and some informal ones. The venues do change a bit and sometimes just using your ears is all that's needed to track down a session.
The programme traditionally comes out very late - usually only one or two days before the festival and we won't really know what's happening until then.
