@user76284: Claiming that "health care is free in UK" is not incorrect by any standards of how the word "free" is typically used: whenever this word is applied to goods or services, it means that "the person who gets the good or uses the service is not required to directly pay for it". It never means that nobody at all pays the bill, because somebody always has to pay.
"Buy one, get one free" doesn't mean that the second piece pops out of nowhere without consuming work or ressources for its production. It simply means that you as a consumer can get two pieces today or the price you'd usual…