Pretty big - it reminds me of that thing that lived in the sand in Return of the Jedi, in that it's a big cone-shaped hole in the side of the hill. It is fenced, but as it's on a steep hillside you'd have real trouble getting suitably substantial capping materials to it unless you can get a helicopter.....
The Lead Legacy was never intended to identify shafts for capping, it was to form a list of the significant mine remains in the Peak which should be preserved if at all possible. Shaft capping has mainly been done by Derbyshire County Council over the years (hence why Ecton hasn't been done) and their priority is making safe shafts that the general public might have access to. I do know that CPCC did some capping work for the National Trust on Ecton, but this was mainly the smaller shafts.
Follow the horses, Johnny my laddie, follow the horses canny lad-oh!