Apologies for the curve ball. I did say that it was from building regs. and it was offered as an example where compliance with an ISO / BS standard is mandatory.
“Have to” applies only if the ISO standard is mandatory. At risk of another curve ball, I was involved with preparing some CE technical files for mobile plant where we could not realistically comply with some applicable ISO standards e.g fencing, so had to demonstrate that other reasonable safety measures were being provided.