Egg, bacon, sausage and black pudding in a roll for £5 from the breakfast menu. Great quality and good value for the location, easily missed tucked away under the canopy of the Great Northern hotel.
My vote for best sandwich In St Pancras/Kings Cross goes to the Salt Beef Reuban from The Kiosk - 1/2 sandwich +plus soup check it out if you're passing through and need a snack!