I would have said late 80's, but just checked some old copies of White Dwarf and it appears to have moved between Nov and Dec 1990. Am I imagining it or did it move back to the Moor for a bit, or were both open at the same time for a while?
I find it's more the weather that effects the crop rather than the variety, I have had really good and bad years with Solent White, this years was the worst yet