Origins of "up the duff"

All the slang sites list the phrase. I saw one or two mention that the word "duff" means a boiled or steamed pudding often containing dried fruit.
Somehow they connected the pudding connotation with the phrase "bun in the oven" ( another phrase for being pregnant ). I dont get the connection so maybe someone else can explain the duff, pudding and "bun in the oven" relationship.

This is all to do with the semi-euphemistic imagery that seems to inhabit the language of things sexual.

Duff is a indeed a boiled pudding. Pudding is also an archaic slang term for penis or, less commonly, semen. The womb/belly = oven metaphor is fairly intuitive.

All of this has lead to the phrases used to describe pregnant women, 'in the pudding club', 'up the duff', up the stick', 'got a bun in the oven', etc.

Gary