It’s actually a question about one disaster movie. I’m trying to remember a black-and-white film about a bomb on a London bus. It was pretty much a forerunner to all those big star-studded epics of the 1970s, eg Airport, where you’d get all the individual backstories coming together for the big disaster payoff. Indeed, in this film the bomb going off was pretty much where it ended.
Does this jog any memories? I’ve Googled but to no avail.