SPS was (is?) a large steel stockholders owned by Corus - their 300,000 square foot warehouse in Bellshill held over 20,000 tonnes of specialist steels for shipbuilding, boilers, pressure vessels, structural sections and loads of different types of pipe. Big boys' Meccano, basically.
The giant warehouse is now stripped, though - but it's still a nice set of buildings if you're into big girders and gantry cranes
The sheds are so massive, the walls are labelled with their compass direction.
BOW - the other factory you saw wasn't a factory, it was another big warehouse - it looks derelict but it's being used by the rail depot.