As far as 1/4 miling goes, there are none as far as I know in the South West, no major ones anyway. I think the main ones are York, Santa Pod and Avon.
I was new to all this 1/4 miling when I first got my lat 172 and then I went to York to the RWYB (Run What Youve Brung) day with a load of others off the site and it was fantastic. It cost £15 I think for the whole day and you can then queue up to get on the strip. I just queued up whenever I wanted thru the day and got around 6 runs in, you can get more in easily depending on how busy the day is. It is supposed to be busier at Santa Pod tho. We didnt have to book, just turn up. When you get on the strip, you line your wheels up on the sensors, wait for the lights and then boot it ! You get a time and a print out at the end of each run which you collect from the timing booth. When I went the day was very well done and I had a great laugh as did most of the people there that day ! I would highly recommend doing it !
As for track days, there are venues all over the UK. I have booked my first track day for April around a sprint track in Curborough but we are looking into booking a track at Pembrey in Swansea, South Wales which may interest you being in the South West.
For more information, check out the Meetings and Events forum,
http://forum.cliosport.net/display_forum_topics.asp?ForumID=7http://forum.cliosport.net/display_forum_topics.asp?ForumID=7.
Cheers,
Dai