Nick Snashall would know EH didn't take management of Silbury back from the NT, it was an arrangement and in August 2000 NT handed it back.
One thing, I am known to be quite a critic of the NT but they swung into action on 29th May 2000 at Silbury ensuring no-one was down the hole when the collapse occurred and roping and organising a guard so no person or animal could get hurt - all this in the dark and semi-darkness - Chris Gingell and co were superb.