I first came across John Dee while listening to Terrence McKenna podcasts, years ago in Hong Kong. At that time I learned he was the original 007 for Queen Elizabeth and an alchemist or more accurately a Sage.
I first purchased this book after listening to a podcast with the author over here, and it took me a long time to read, as it's crammed with esoteric knowledge that is vast, visual and layered. I'll never be able to retain and recall that kind of knowledge, but I know a man who can, so he's reading this book next.
The main point of this post is because the security services are the most concealed group for using all kinds of magick from Chaos to Enochian or Operative. While researching the subject on Wikispooks I discovered that the article on the occult and SIS was written by none other than former Home Secretary Michael Howard.
If that whooshes over your head there's not much for you here, except to add that I don't think the full story of John Dee is currently that accurate, as he was careful who he told what.
Also, if we look at another SIS asset who was into the occult, there's Aleister Crowley. Both he and John Dee died quite impoverished and so there's that when entertaining thoughts of exploring occult rituals and so forth.