when we were in the UK a few years ago, a couple of the places we stopped for lunch had mustard on the sandwiches, but it wasn't like French's or Heinz mustard we are used to here...it was almost like actual mustard seeds, blended in an almost butter like spread...perhaps similar to the kozliks...when you bit into a mustard seeds, it had some zing to it...they didn't put so much on that it would ruin the sandwich, but on something like a ham and swiss, it added some nice zest.