I've just had a conversation with TNA at Kew - and surprisingly they appear not to have any information or links to names like British Sawrex or Sawrex Glass - rather disappointing. So rather stumped for the time being, but will persist if I can think of a different angle. If you Google, you get something called - The Sawrex Glass Marketing Co., Ltd., although now dissolved, but whether they had connections with, or were one and the same as British Sawrex, I don't know.