When I started diving in the 70s with BSAC in the UK a diving medical and recent chest x ray were required in order to start your training. Once you were a member of a branch and diving with your local club, you were required to get subsequent medicals every 5 years till age 30; every 3 years till age 40 and an annual medical each year post 40 years of age. There were no insurance liability policies for instructors then and the point of the medical was to let each individual know that they were healthy enough to dive safely, without medical risk. The club I was in till I came to Canada in1982 had over 100 members who all followed the rules without thinking much about it, because it was a way to keep "the odds" stacked in your favor... no medical contraindications = safe to continue diving. The "mindset" now seems to have swung due to the increased litigation and influence of liability insurance companies to view the medical sign off as something onerous that is required, rather than "is it medically safe for me to dive"....just a thought