Oh bleah, I just read that wikipedia link - it's sweet? Heresy!
Seriously though, sweet pickle relish is practically the ultimate betrayal: it looks exactly like ordinary pickle relish (which is freaking delicious), but if you make the mistake of putting it on your hotdog/sausage/whatever by mistake, you discover it is exactly not the flavor you ever wanted on whatever it was you just put it on. Can't spit the stuff out fast enough!
Of course I have this thing where I think that foods not explicitly designed to be desert products should never be sweet (at best they can be tangy, but sweet is right out), but still, there is just no excuse for sweet pickles.
Branston Pickle therefore sounds like an unbelievably nasty thing to put on a sandwich - I will stick to putting pure horseradish on mine (so delicious!).