Bretwalda is a Diplomacy variant created in the mid-1990s by Geoff Bache. It is a 9-player game with the players representing the kingdoms of Britain beginning in 620 A.D., including Wessex, Mercia, Dalriada and the Picts.
I noticed in 2006 that the information on Bretwalda seemed to have disappeared from some of the Diplomacy websites, so I dug out the stuff I had kept, and reconstructed the map and rules information, and I'm putting them up here for a resource for anyone who is interested. I hope Geoff is ok with this, and would be happy to hear from him whether he's in favour or not.
Large Map: (2.4mb)
PDF file including map, variant rules, map key and area abbreviation index, and historical background: (700k)