As an ex-Surrey dweller, I used to find very cheap spaces on farms. Most will either let out units as a revenue stream or will be willing to listen to offers. Because of the amount of unused outbuildings on farms coupled with a growing number of serviced offices in the region, and because they're typically off the beaten track, there are some real bargains to be had.
I once had a three bedroom bungalow that couldn't be lived in as it had been redesignated as commercial for around ã150 per month, power and water included. My mate ended up with a huge canteen that used to serve a small industrial estate for less than that!
As long as you don't look like trouble, some rural places like to have people coming and going as it adds to security. Just be friendly, go asking around and doors open!