Kippers and sardines are both small herring.
Kippers are split, gutted, butterflied and cold smoked. They tend to use slightly larger fish for kippers.
If you get the ones marked “Kipper Snacks” or “Kipper Fillets” they will also be headless and tailless and in that fashion they fit nicely on a sandwich. (Like toasted Rye with a slice of tomato and very, very thin onion.)
Saturday Breakfast | Baked Kippers and Eggs with Soldiers
http://foodieclaire.wordpress.com/2012/10/20/saturday-breakfast-baked-kippers-and-eggs-with-soldiers/
Thank you for the clarification.