Recently in the UK there has been the case of David and Ed Miliband competing to be leader of the Labour Party, which many see as an act of treachery on Ed's part.

It seems like something that must have happened before, but I can't think of any cases. Obviously competing against family members is kind of the natural state within hereditary systems, but I was wondering about elected posts, historically (especially in the UK, I guess, though wider examples are welcome).