It's cereal-based. Claudia: Black pudding starts with a dry mix of pig blood, seasoning, rusk, and oatmeal. And when we say dry, we mean this. Seriously? [laughs] Richard: Yeah. You'd never guess.

Pigs in blankets and Christmas pudding are two festive staples that diet expert Tim Spector will never allow to be served on the day. The scientist, who co-founded the popular diet app ZOE ...