Like Smiling Sheep, we move to the west country from greater London just over 4 years ago. We had been thinking about it for years but it took a year of active looking before we found the right combination of house, land and location.(Mind you, my husband is very fussy when it comes to location).
We found the best estate agent was GTH (Greenslade Taylor Hunt). They really know about land and what it can, and cannot, be used for. Their prices are realistic and their staff helpful and friendly. Having said that, it is worth looking at lots of different properties to work out what is really important to you. Prime Location is quite good for smallholdings because you can enter "acres" as one of your search fields. Also, Rural Scene.
Good luck and let us know when you have somewhere.