progress at last!
This decanter is a cut glass horseshoe shaped decanter with an engraved scene. The one in the Stevens and Williams book is a cut glass horseshoe shaped decanter (same shape) and similar design but the cutting is different and the panel is enamelled one the one in the book.
Both contain the frosted plain glass fox head stopper!!
http://www.the-saleroom.com/en-gb/auction-catalogues/andrew-smith-and-son/catalogue-id-srandr10022/lot-7639ee4e-1e6e-4dce-8e2b-a43c0174e4e8Click on the picture for it to come up in the correct shape

So ... do we tentatively conclude that since one is in the book as Stevens and Williams with the artist specified, and that they are both the same shape though different cutting and one is engraved instead of enamelled, and that both contain the frosted fox head stopper, that the frosted fox head stopper is likely to be from Stevens and Williams? Therefore if my blue frosted fox head on my stirrup cup is the same design fox head, then it is likely that the stirrup cup might be Stevens and Williams and the fox head made by them? This is made more likely because the design of the stirrup cup and the feel of the glass is very much in the vein of other STevens and Williams pieces I've owned (goblets with horses in stems) and alabaster pieces.
The book appears to describe the picture in the text as ' In the works museum a "horseshoe" whisky bottle survives, with... ' It goes on to say
it is partnered by a goblet with a similar picture.
So I think it is reasonable to conclude that the fox head was made by someone at Stevens and Williams. There are two known stopper both in clear frosted, one broken blue one described as a stopper but I think it actually came off a stirrup cup, and my blue stirrup cup fox, as well as one grass green fox on a stirrup cup that I think is probably the same shape (bad photo).
So ...
who made the fox at Stevens and Williams? how is it made? is it pate de verre? or is it cast somehow? It's massively heavy.
The only spanner in the works is this
http://www.glassmessages.com/index.php/topic,56463.msg320124.html#msg320124Charles Hajdamach shows in 20th Century British Glass page 115 the same cut decanter as the one in the Crystal Years, with an enamelled panel on the front but a different enamelled picture to the one in the Crystal Years (same theme/style etc though) with a stopper that appears to be cut to match the decanter.
Were the ones with the fox stopper specials?
m