I went to St. Austell brewery last summer when we were holidaying in Cornwall.
They do a very good tour indeed. Started off with an introduction and history of the brewery, then a good tour round the building, which is the original purpose built Victorian building. Each part of the process was covered and the staff were very knowledgeable. Ended up in the bar where they let you have tasters of each beer, and a couple of vouchers to exchange for pints, IIRC. I recall a few very nice pints of Trelawny. :drink: They have a huge brewery shop and are also a big wine merchants if the grape appeals too.
Closer to home, the Hog's back brewery in Tongham. Don't, whatever you do, drive, though. Most of our party did, so it fell to the two of us who didn't drive to ensure the freebies didn't go to waste. :drunk:
Even closer to home (a short stagger for me) is Triple fff brewery, and they do a good tour, I think, only for groups, but they also have an open day each year with tours, live music and food which is worth a look. On a much smaller scale than St. Austell, of course, but still just as fascinating.
Keep meaning to go to Hook Norton sometime, as they apparently do a nice tour.
Highly recommended, I'd say. It was seeing what makes a brewery tick that got me interested in brewing my own. :thumb: