John:
The 'Empire' action was patented in 1910, and the first prototype (no. 57740) was started in feb 1910 but not completed. The first Empire to be finished (no. 57894) was started on 15 March 1910 and completed on 15 May of that year. From 1910 to 1919 about 30 per month were made (~360 per year) with less during the war years. They were made by Greener up till 1965 when Webley & Scott acquired the firm and stock, and finished-off another ~170 up till 1971. A few short-bar Empires were made in 1925 apparently. In all, some 17,268 Empires were made by WW Greener between 1910 and 1965.

Info from Graham Greener's book, "The Greener Story" Chapter 10: The Emperor and Empire Models 1894 - 1971, pp127-130.

I should add that anyone who would rather spend their spare readies on a box of Bud than buy this book is a DUNCE!