Of course I've snipped a live cable, a few times over the years, don't you keep a pair of old snips in your bag for this purpose when you aren't 100% sure its dead, we call the snips chancers.
As for people losing out on money, I was on about if the spark that turned up with the lads said he wouldn't get power on then no-one can do any work. Nearly all tradesmen are self employed, only the crap ones are cards in nowadays so if you don't work you don't get paid. Not only that if the job isn't competed on time then the contractor probably won't get any more work of the main contractor/insurance company or whatever and that can be worth hundreds of thousands of pounds.
So to say "not my problem" about energising a supply will do you no favours whatsoever. I have my limits about what I will do - like crawling in rat ---- - but being scared of the electric police isn't one of them.
As for my opinion on the H&S brigade, when I've worked on bigger sites in the past I've found they run best when the site manager has cleared off for the day, everyone is just able to get on with things away from the constant interference, they don't add anything of worth to a job. Hasn't a contractor just been killed on the Everton stadium? The H&S must be off the scale on that job but it still happens, a hi-viz didn't do much to help him.