Note: This is not Part-P style stupidity. I've just uncovered why one of the lights in my son's en-suite wasn't functioning. Somebody had wired up the light with a choc-block in an enclosure - but had forgotten to tighten the screws (Yes, I know, it's a stupid mistake; but how many of us are /absolutely/ convinced that we never make a stupid mistake?)
The result was a loose connection with a high junction resistance - so the choc-block turned brown and melted. In our case, the wire then pulled out of the connector - but I can easily see how the enclosure (or surrounding dust if no enclosure) could have started a nice little fire.