When we were stationed in Europe in the Navy, we had the chance to visit England. We saw them eat some similar breakfast foods and some different from us.
They will broil tomatoes and mushrooms at breakfast - great for all phases of South Beach! They also eat baked beans - now I don't know of any ready made US brands without sugar (at least I didn't see any in Kroger's last night) but I think I saw a SBD recipe for baked beans on this forum.
They also eat smoked fish. They call them kippers or bloaters, all herring, name depends on how long they have been smoked and salted. I don't know if the real thing would technically be legal on SBD, haven't seen any in the States. Once in a while, though, I do see canned herring fillets called "Kipper Snacks." Love 'em! Canned sardines would work, so would any fish fillet broiled in the same pan with your tomatoes and mushrooms! Might not be authentic British cuisine, but a good phase 1 breakfast for those who want a break from eggs!