Bubble & Squeak really is a funny name. I've never heard of it before.
But, speaking of leftovers... tonight I watched one of Paula Dean's shows on Food Network and she made a really tasty looking (and rather decadent... as her recipes often are) casserole with leftover mashed potatoes (the leftover mashed potatoes I guess were the original inspiration for the dish). It was a layered casserole with the bottom being the mashed potatoes, then covered with sour cream, then covered in onions and peppers sauteed in lots of butter, then cheese, then sliced roasted potatoes and then I think it was all repeated once and topped with cheese. Then she baked the whole thing. It definitely looked like comfort food.