Thank you all - I do intend to get a sparky to do the wiring into the
fusebox, but regardless of regulations etc. etc. I intend to cable it
through myself, and if appears simple enough, to the isolator switch
in the bathroom and then the shower. The only work I can really see
for a sparky is attaching the cable for me to a fuse box (which itself
looks about 30 years old - highest breaker is 45A which I'm fairly
certain feeds the oven)