I know that epi-pens are the last resort. Everytime my allergic reaction is assessed the Doctors tell me this.
Even if I presented at hospital with anaphylactic shock they'll try the anti-histamine tablets (or injection of such) first.
Not naysaying your information Hawk; and I agree that in the UK we don't have many poisonous snakes outside the folks who keep them as pets or in zoos, the adder is pretty much it, yes ?; but sometimes we of this bushcraft community need it kept simple.
It would be appreciated if we didn't leave folk with the impression that any allergic reaction and it's safe and allowable to find anybody's epi-pen, or even one in a first aid kit, and administer it.
Adrenaline administered like that is a horrendous shock to the body; first aid courses make a point of saying that the aftermath can be worse than the cause, and first aid is first do no harm.
Interesting to read the 'legalities' of the situation though, and I'm pretty sure that in a survival situation somewhere remote from modern medical facilities, knowing how and when to administer such things as an epi-pen, or snake bite anti-venom would be a crucial skillset.
cheers,
M