Good BBC magazine article on are Jaffa cakes cake or biscuit?
http://www.bbc.co.uk/news/magazine-38985820
Also Frances Quinn, GBBO 2013 winner, makes a rather large Jaffa cake. The article had a video clip of her making it. Later in the article there's another clip of a Guinness World Records representative measuring the Jaffa cake to see if it sets a new record.