It is pretty much 20 years exactly, my OH worked on the site doing catering for them. Not my OH then, but my OH now, if you see what I mean!
My old boss went through exactly the same thing, got a place on the edge of a development with great views. 10 years later they built on it, her response was "We bought the house and garden, not the fields around it". Otherwise Castlefields would never have been built, as it spoilt the view of others. Hell, nowhere would be built! As long as there is as much green space to houses as castlefields itself has there is no issue in my eyes, but looking at it they only have green land on the periphery of their estate really. I guess they sold it on the surrounding area, that wasn't theirs to sell.