You didn't answer the question. It just kind of sounds like something the Brits might have made up. I would never put them on a slice of buttered bread. In fact, I don't eat them...too sweet.
In the 1920s Omar and Cora fanning canned sweet and sour pickles, The story goes that they were so good people bartered bread and butter for them. another story is that during the depression sweet and sour pickles on bread and butter was a cheap thing to eat.
Randy D 