Before I retired, I recall coming back to the telephone exchange after lunch and smelling burning plastic.
Cursing myself for leaving the soldering iron plugged in somewhere I duly went to investigate.
Not the soldering iron, but the wall end of another extension lead.
The ELCB/RCD attached permanently to the end of the reel, and plugged into the 13a wall socket had melted and dripped plastic onto the floor. Worryingly, it was just sitting there smoking gently, but hadn't tripped.
When I mentioned it to our PAT tester, he commented that it happened quite often with that make, replaced it with a 13A plug and suggested I used it with a separate ELCB adaptor to conform to the H&S rules.