Hi Chipmunk, and welcome to ECN. Glad you've found plenty of topics of interest here.
I've seen zipcord used for a variety of things before, but not for a washing machine!
From memory, I think Maplin used to stock a few different zipcord types, rated between about 60 and 100V.
Bridged circuits is something I've come across quite often. You go along the board, pulling fuses or flipping breakers one at a time and the outlet you're testing remains stubbornly hot. Then you just know
you're in for a fun time trying to sort it out.....
Those pics look all too familiar. From the box styles and cables that looks like the original wiring dates from the 1950s/early-1960s, with the usual more recent hacks and modifications.