bluebell56: I have seen this clue previously, and I wonder if the figure of 200 square miles could be incorrect. 200 square miles equals 128000 acres, which is a very large area of land. Cotgrave Country Park covers 200 acres; could that be what the setter meant?
from 1906: "THE district known as the "Dukeries," begins about twenty miles north of Nottingham, and extends about ten miles in the Worksop direction, its average width being about five miles. "