Nutloose - I thought the same, but it turns out there are two different Chetwynd sites that share the same bit of land.
The Reserve Estate (e.g. Royal Engineers and HMS SHERWOOD) is, I believe, staying put and not closing. What is going instead is the very old part of the barracks that is in pretty poor condition. Having done a number of courses there recently, that part of the site is not in a good way.
What is more interesting is going to be whether any developer wants to buy doubtless contaminated land, with a veritable rabbit warren of tunnels beneath them from the old ordnance factory that dates back to WW1?