Wait a sec- BDW, aren't you from Scotland, home of the deep fried hamburger?
Yes I am and our traditional fast food outlets (Fish and Chip shops) do serve hamburgers dipped in batter and fried. They are not very nice and I certainly would not eat them. ;)
The reason they do it like this is that our "Chip Shops" always tended to have just the one means of cooking things and that was in their large deep fat fryers. They even used to fry pizzas in the fryers ... yeeeuch!
Many of our fish and chip shops are now doing it better but there is still no shortage of the old ones around and they do generally serve excellent fried fish with hand-cut chips. None of the skinny little McDonald's style processed French fries for we Scots (or Brits actually). It is also worth noting that our fish and chip shops almost exclusively cook the food in the front shop where customers can watch it being prepared so there are no surprises.
The deep fried Mars Bar thing is a publicity gimmick. You can find them on occasion but if you visit 100 fish and chip shops in Scotland you will be lucky to find one of these serving them and anyway, is it that much different from Baked Alaska? ;)