Harry Macdonald:

Good point AJJewsbury, but can anyone think of a requirement in the current Regs that is actually prohibited in an earlier version.

If not, then an installation to the current Regs would satisfy all of them.

This is actually rather complicated, since the Regs are not normally legally binding. They are a standard, compliance with which is considered to be a presumption of meeting the safety requirements/duty of care. Compliance with a more up to date standard is always considered to be as safe as (or possibly safer than) compliance with the original standard and is therefore acceptable as an alternative to an earlier standard in such an instance, on the basis that standards never reduce safety when they are revised. However where the legal text specifically states a particular edition of a standard this may not be a valid assumption. It doesn't even need to be something required/prohibited but just a difference in the requirement that means an installation meets a later standard but not an earlier one.

The safest approach is to ensure that the installation meets all editions of the standard cited, though if there are contradictions you have got your work cut out.

Harry Macdonald:

Good point AJJewsbury, but can anyone think of a requirement in the current Regs that is actually prohibited in an earlier version.

If not, then an installation to the current Regs would satisfy all of them.

This is actually rather complicated, since the Regs are not normally legally binding. They are a standard, compliance with which is considered to be a presumption of meeting the safety requirements/duty of care. Compliance with a more up to date standard is always considered to be as safe as (or possibly safer than) compliance with the original standard and is therefore acceptable as an alternative to an earlier standard in such an instance, on the basis that standards never reduce safety when they are revised. However where the legal text specifically states a particular edition of a standard this may not be a valid assumption. It doesn't even need to be something required/prohibited but just a difference in the requirement that means an installation meets a later standard but not an earlier one.

The safest approach is to ensure that the installation meets all editions of the standard cited, though if there are contradictions you have got your work cut out.