You can also Google - "land for sale UK" or "Woodlands for sale uk"
Auctions are also a good place to buy - although expect to pay way above the "guide" price, as they are deliberately priced low to get interest. I have just paid 4x the guide price for a small piece of land at auction. But it was well worth it for what I want.
Google "Future auctions" to get the details of those being held in your area.