There is a lot of overlap in todays Plumbing between Gas Regs, Building Regs, Water Bye Laws, British Standards and Wiring Regs its getting so you have to know nearly all of them or at least have a basic working knowledge.
I once was showing a class of adult Trainee Plumbers some of the electrical things they would probably be required to do as part of their job. The City and Guilders invigilator went mad. Basically C and G Plumbing really had nothing to do with electrical work. He was right of course.
My argument was, that that was out of date, in reality they would probably touch on electrical work quite a bit, so a basic working knowledge of it was at least useful.
You tell me which your most likely to do now days as a working repair Plumber, mend a boiler or dress up a lead bay?
The guys I was showing intended to go and get jobs where ever they could get one, not work for just specialist lead work companies.
Its not that there isn't a lot in Plumbing without touching electrical stuff, its just that invariably you always seem to come up against it at some point. Without a decent working knowledge of it, your going to be a danger to yourself and the customer.