That would be the Goodwood estate near Chichester. I know someone who tried to get access to the land from one of the Keepers & it did not go well.....
Saying that there is some nice woodland that some of us go to that is a few miles to the east, such as Eartham Wood; which is a bit North of Fontwell if you know what I mean, Both the areas in the red boxes in the attached map are good & if you walk/bike in a ways then you are not disturbed.