Rebecca - as you already know, here is the information from Diageo - we are posting for all to see!
Rebecca, The White Horse figure has come in different sizes and materials over the years and those that are as large as the own and have purchased are quite rare. That particular design of figures was in use for many years ranging from the 1920s to the 1940s. So, your horse could date back to the 1920s although it's difficult to say for sure. We suggest you contact BBR Auctions for a valuation - onlinebbr.com " ~ Diageo Archive Department