with respect I think we might be getting a bit carried away here and also confusing what Chris said about America with the situation in the UK. I'm sure that there are people out there worried about doing/supplying stuff in case they get sued, but I suspect that they are victims of media hype and poor advice rather than acting rationally.
Firstly the consent versus common assault part of things, this is very old stuff, part of common law in England and Wales ( can't remember how Scots law deals with it) So the idea that a legally competent adult can choose to refuse treatment is long established in law, nothing to do with any current or recent government. There are some changes working their way through parliament now in relation to the " body parts" scandal. Presumably as a first aider you're not going to be keeping body parts for any purpose :shock: .
It makes good sense practically as well as legally to ask the person if they're happy for you to carry out a particular procedure or use a product. Decisions about what you should do always carry a risk/benefit analysis: "I've got this tape to hold the dressing on so we can protect the wound from contamination as well as help to stop the bleeding, do you know if you're allergic to it? No, OK there's always a chance you might be, are you happy for me to proceed? " seems pretty sensible to me. Obviously your unconscious person can't give consent, you just have to do your best.
Secondly the issue of duty of care. Registered Nurses, like me, have professional rather than legal obligation, ie I might be struck off the register rather than sent to jail/fined if I don't provide the care.
Here's the form of words used by our professional regulators, the NMC:
"In an emergency, in or outside the work setting, you have a professional duty to provide care. The care provided would be judged against what could reasonably be expected from someone with your knowledge, skills and abilities when placed in those particular circumstances."
I think this second sentence would probably apply to anyone responding to an emergency, but remember you're not expected to put yourself in danger.
This area of law might appear vague but my feeling is that actually does expect us to behave with common sense, no point in preparing to an emergency tracheotomy with your SAK, if you've only read about it once on a website. It might help to think of yourself being physically incapacitated and in need of first aid finding yourself at the mercies of some well meaning but not well informed passerby. " Honestly, I don't think I'm going to need a tourniquet for that cut....."