Nigel - When I first read your book, that piece on p50 elicited a huge "WOW! - BRILLIANT!". I had already thought that the most likely attribution of this rather mundane vase was a Continental glassworks via a factor like Lang, and hadn't considered the possibility of a British maker. Only two criticisms:
You assumed that we all knew Jack L. Barnett Ltd. Was this firm an associate of Barnett & Foster, the big Bolton and London bottlemakers who relocated to Wellingborough, or quite a different company? Did they manufacture glass themselves?Your final few words after "thus". What you say may be true, but I would have preferred "thus escaping purchase tax."
Had you asked me before I read this topic, I would have replied that a Bagley attribution was impossible. Why on earth would a modern sophisticated and successful pressed glass department of a large bottle works produce such an old-fashioned design? I will be interested to see Angela's evidence.
Bernard C. 
Bloomberg says Jack L Barnett are importers and distributors, not manufacturers:
https://www.bloomberg.com/research/stocks/private/snapshot.asp?privcapId=561022 Jack L Barnett, headquartered in Leeds, operates in the logistics sector of industry, delivering glassware products to retailers in all areas of the United Kingdom. The company is the primary distributor for JG Durand, the world’s largest glassware manufacturer. Other companies with which Jack L Barnett operate include Luninarc (sic), Arcoroc, Arcuisine, Crystal D’Arques and Arcopal.
A bit more digging revealed the information that Jack L Barnett was the subject of a management buy out by the Managing Director and 2 other people in July 2000 and the new business was named Brands Home & Leisure (BHL), which in turn was taken over by Thermos in 2017 (for whom BHL had been the UK distributor for 16 years.) Meanwhile the original Jack L Barnett Ltd company had its name changed on 20/05/04 to ARC INTERNATIONAL TABLEWARE UK LIMITED under the signature of Philippe Durand. They are still in business too.