I found this photo in an old packet of prints. At a guess it is around 15 years old as it's from a camping trip in my VW, and I've not been anywhere in that for over 10 years (still for sale!).
Wessex Flour Mill is still a working mill - I could give you some history, but it's much better on their own website.
It's an odd looking, and slightly posh building. Those arches over the top of the square windows are a decorative feature I've not seen before.. The whole lot looks a bit spruced up to satisfy the good citizens of Wantage to me, but then we are a long way from dark satanic mills, so perhaps it's always been pretty?
I like that ugly pipe sticking out of the top though.