I found this while I was trawling through a second hand book shop - The Shell Guide to Gardens. It looks like oil companies have been trying to associate themselves with anything that makes them appear green and natural for quite a while.
It was published in 1977, and the inside jacket describes the book like this, "This book has two parts: a concise but colorful and informative history of four centuries of garden-making in Britain and Ireland; and a detailed but convenient guide to over two hundred of the finest, though not necessarily the best known, gardens open to the public."
I'll be honest, I haven't read it. It's a little dry, and despite the claim that it's a colorful book most of the pictures are in black and white. Perhaps I should drop this early example of green-washing in a recycle bin. ::Flickr