At QE it’s just as much about the huge swathes of the Park which are designated SSSI. Ancient field boundaries, etc… run through the park, and any trail users could cause considerable damage to these quite rare features. That’s why there’s not much legitimate riding in the Park itself, there’s simply too much conflict of legitimate use in too small an area.
Simple way round it in that particular instance is to uae it as a warm up before heading out on the South Downs. As others have said, there’s plenty to ride. Alternatively, ‘100 Acres’ up the road near Boarhunt has on one side of the plantation an open access policy. I still have the letter from the FC I received a few years ago in response to enquiries telling me “as long as you are not carrying power tools in there and felling major trees, do what you want with regards to trail building.”
Time and health constraints prevented me doing anything, but basically license for singletrack creation a 10 ish mile ride from QE Park. Reinforces that the Rangers do have the trail users best interests at heart, they just have to work within the constraints of the land.