Thank you, Paul, that's been a great help.
According to http://glasscottage.net/pressed-amberina/
Scotney and Earnshaw were listed in the ‘Pottery Gazette Diary’ under “Agents for Foreign Manufacturers” from 1884 to 1901, and specialised in the wholesale distribution of “American Tumblers”.
They also registered design number 64088 [and according to Thompson, 64087] on December 22 1886, 64088 being the “Daisy and Diamond Pattern” [for the decoration of Glassware], and many pieces of pressed glass in this pattern have been found bearing Scotnney and Earnshaw’s registration number, and since Scotney and Earnshaw were not manufacturers… we did find a link between them and Hobbs, Brockunier & Company of Wheeling, West Virginia, who seem to have made articles in this pattern for export.
shows an advert [dated 1889] for C. Morton, The City Type Foundry, 167, City Road, London, E.C. , promoting “Morton’s New Ornament Book” whereby “Export Orders receive prompt and careful attention. All Type packed in tin or zinc lined cases and shipped by our Shipping Agents: Messrs. Scotney & Earnshaw, Water Lane, Tower Street, London, or by customer's Agents.”, so it would appear that Scotney & Earnshaw were agents for a diverse range of goods in addition to glassware.
A quick scan through Thompson has also revealed the flowing Scotney & Earnshaw design registrations:
RD 73836 of 17 May 1887 (pattern for the decoration of table glass ware];
RD 310924/5 of 16 December 1897 (where they are described as ‘Glass Maker”).
Despite their appearance in the registration lists as ‘Glass Manufacturers’ or Glass Maker’ I can find no hard evidence so far that they were actually had a glass works producing their own glass articles, but at least it’s nice to find, among the plethora of agents, importers and the like who registered designs, another who can be linked to actual manufacturers of glass in one or more specific locations.
I will try contacting the Heisey Museum to see if they can provide more details about the connection between Heisey and Scotney and Earnshaw.