It doesn't look like they were the same company Frank.
Duro-ray was a limited company in its own right, and is now called B. & S. GLASS INDUSTRIES LTD.
Date of Incorporation: 31/07/1928 Company No. 00232408
Date of name change: 30/04/1992 Previous Name DURO-RAY LIMITED
Address: 47 SUTHERLAND ROAD, WALTHAMSTOW, LONDON, E17 6BH
No mention of Duroglass in their historical details. [Source: Companies House register)
"Duroglass" also "Durosil" also "Duro Sil R" also "Duroven" Duroglass Ltd., 2/3 Norfolk Street, London.
Makers of lighting, scientific glass, fireproof glassware and ovenware.
[Source: British Glass after the War, Glass Museum http://www.glass.co.nz/trademarks.htm
I can't find them in the online register, but I did find an obituary of their former Chairman, Douglas Heriot Baird [in PDF format with some interesting glass info: http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=JR9400000562&JournalCode=JR
and a mention of Duroglass Ltd in the Victoria County History, A History of the County of Essex: Volume 6, published 1973 (see online version: http://www.british-history.ac.uk/report.aspx?compid=42779
, which quotes the Walthamstow Post, 22 Mar. 1951 as its source for the following:
Duroglass Ltd., laboratory glassware, built a factory in Blackhorse Lane during the First World War. It closed in 1926, but reopened in 1932 to produce lighting glassware and, later, television components. The firm ceased about 1965, when the premises were taken over by Industrial Glass Co. Ltd., which itself ceased by 1968.