many thanks TC.......so not really like Bakelite then, and more of a modern fibreglass material. Bit disappointing, as I'd hoped this shade might have been from the 1930's or thereabouts.
Details of the US registration, as shown in your link, are for 1969, although I see it also comments that the first use of the product was in 1963, so I'm not quite sure about the intervening years - although bearing in mind how mine is marked then obviously at some point in its life there seems to have been a licence granted for UK manufacture of Duroid.
However, for the time being it doesn't really help with knowing who made the glass, so will hope perhaps to find a catalogue or book image some time. Probably looks good when 'all lit up'. thanks again.