Steve,
I’ve had a look at VHGMC archive stuff and a few other sources and your Webb Witch appears to date after 1936, yet it has the ribbed rear roller meaning it was a later production machine, but it has the earlier older style handles later changed in production to the crossed handles. From that information and if we had a selection of brochures then we’d probably be able to date it to within a few years!
An interesting early-ish machine and apparently not many about.