UK-wide????
So far nearly all in England, largely in the south, one in Wales.
You can get details of most Scottish festivals via www.tmsa.org.uk
I haven't been to them all yet by a long chalk, but my favourites so far are: Glenfarg, Linlithgow, Lomond, Stonehaven, Girvan, Innerleithen and Both Sides the Tweed (which will be in Selkirk this year; it moves around every couple of years) All of these are weekend festivals in lovely locations, with very friendly natives. I gather Orkney and Shetland festivals are pretty wild, and it helps if you play fiddle at frenetic speed!