Thanks for the Black Bun information! The filling in the linked recipe has a lot in common with the Christmas pudding recipe I use.

And yes, Spotted Dog and Spotted Dick are the same thing, as is Plum Duff. They're all essentially dough with currants.

A lot of folks have a bad impression of suet because they think it's the greasy beef trimmings often sold for feeding birds. Proper suet is the fat from around the kidneys, which is hard and white with an almost crumbly texture. I freeze it and then grate it when using it in recipes.