Hi Mike,
thanks for that, looks like we're both confused then.
Maybe rather than a set system the BNA treat each case on it's merit as t'were, aka pay the least they can get away with. I asked as was hoping to be able to go to Mark Turner and thus presumably the local Council, who I guess are the true owners of the old Mercurys with a clear easy option, oh naive fool that I am haha.

Somehow I knew it couldn't be that simple..

cheers sir.