In Newcastle and across the Northeast the bread is a stottie, and it is the heaviest, densest carrier in the whole bacon family. A stottie cake is a large, flat, round loaf with a thick, close, chewy crumb and very little air in it, usually cut into a substantial wedge and split rather than served as a small individual roll. It has real heft and a serious, almost rubbery chew, and it eats more like dense bread than like anything soft and pillowy. Where a bap surrenders to the filling and a barm flattens under a hand, the stottie holds its shape and makes you work for the bite. That dense chew is the variable that makes this the Northeast's version; the bacon inside is the constant the whole country shares.
The stottie's density changes both what the bread does with hot bacon and how much you can put in it. The close crumb resists soaking, taking up far less rendered fat than an open bap would and staying chewy rather than going translucent, so the bacon's grease sits more on the surface than through the bread. That resistance is why the stottie carries a heavier filling than the soft rolls: there is structure to spare, and a few extra rashers do not defeat it. The build is the usual discipline against a tougher bread: butter the cut faces so the fat does not pool on the dense crumb, lay the bacon in hot, keep sauce inside so it does not run off a surface that will not absorb it, then close it and bite through a roll that gives slowly. The reward is a long, dense chew with the salt and crisp of the bacon held firmly inside it rather than melting into the bread.
Out of the Northeast the same sandwich answers to other words. It is a bap across much of England, a barm in Lancashire, a cob through the East Midlands, a batch around Liverpool and Coventry, a morning roll in Scotland, a butterie in Aberdeen. Drop the bread question and it is a bacon butty, or a bacon sarnie said casually. The fillings stretch the way the names do, and the stottie's heft invites it: a fried egg with a yolk to be managed, a sausage with or instead of the bacon, the brown-against-red sauce question each kitchen settles its own way. Those deserve their own articles rather than being crowded in here.