I can beat that Allen.
Yesterday found a four storey shop with a single staircase.
It had originally had a mains powered alarm system with break glasses, bells and mains magnetic hold open devices on the staircase doors. At some time in the past (probably 20 years ago looking at the panel) someone has installed a 5839 part 1 system (effectiely L4 plus a few detectors). And they had kept the old 240 volt system in place and live, installed a relay interface between the 5839 and the 240 volt system so the doors, still retained by the 240 volt magnets, close on operation of the 5839 system.
I was called in because an earth fault had occurred and the metal case of the 5839 system was giving people shocks. So they wanted an risk assessment to identify how it should be replaced. I found the casing live at 240 volt potential and called in an engineer.
The last company to maintain it had not commented on any variations.