Hello, This is an early version of a Horace Fuller made at the Feedex Works, Horsham, Sussex. For this to be Granmothers Grandads, that may be pushing it a bit (no pun) but it is earlier than the popular one from the 1950s. I suspect this could be early post second world war ie mid to late 1940s but I am not sure when Fullers started production.
I have never seen an early one with paint on so these may pre-dated the orange and green colour scheme of the later hoes and drills. Equally whilst the handles are of the same design as the later ones I have not seen one of these earlier types with the Fuller transfers on. I recently cleaned some hoes blades from a Fuller hoe and found them to be stamped Fuller so a diligent look in this area may confirm the brand
A nice find
Regards–Steve