I'm not sure how to link to a pdf, but the June 2010 IAOPA has an article:
"Getting the Lead out" (pages 38-39)
You should be able to google it.
It says only two avgas refineries are left in Europe, and neither is in the UK.
Perhaps the lack of competition, and transport costs, are factors here.
I don't know what my linking problem was earlier, but this link seems to work now:
http://www.iaopa.eu/mediaServlet/sto...n10/p38-39.pdf