You don’t have to be an emigre to remember them. I lived in Leeds and my dad was a builder. The best thing for laying flags is clinker from a chain grate stoker, and the mills just wanted rid of it, so we’d turn up in his waggon and just load up. I was only little, so got to look at the engines. Remember that the national grid and electricity generating infrastructure back in the 50s was not as it is now, if you already had an engine, boiler etc, it made sense to keep it.
The air quality was a different matter. In Pudsey, which nestles between Leeds and Bradford, the pigeons had learned to fly backwards to keep the soot out of their eyes. Seriously, all the buildings were black, and the haziness in many old photos isn’t due to poor photos, it’s the air quality. Even into the 70s in South Lancashire we were regularly sent home from work early because of fog, the turn in to the car park off the main road was marked by watering cans full of paraffin with rags stuffed down the spout blazing away.