This happened while SWMBO and I were out.
Older son was vacuuming the stairs (unusual, I know, but he needed to earn some cash). He was using the Henry, and took the end pipe off the give him a bare pipe with which to coax something off the carpet.
Henry was safely at the bottom of the stairs. He dropped the hose and pipe, and the pipe landed, end down, on the power cable. Flash, bang, pop! The sharp edge of the pipe severed the cable - both cores and all but about 25% of the outer insulation. MCB popped.
He hadn't a clue what to do, and was also worried by the beeping coming from my workshop (the power circuit on that side of the ground floor was now dead, and the UPS powering one of the servers, the one in the workshop, had leapt into life).
He was quite shocked (although not electrically). SWMBO found him standing in the hall about 10 minutes later, with not a clue what to do about anything. He wouldn't know an MCB if it bit him!
I'll fix the cable tomorrow - the cut is near the plug end so I'll probably just truncate it as long as the cable is workable.