In England and Wales the RRFSO applies in full. If the construction is self-contained, then the HSE enforce the RRFSO, if the construction affects an occupied building then the FRS is the enforcing authority. In the latter option the FRS also enforce 3 regulations under the CDM regs.
In reality, most of what the CDM covers will take account of the normal requirements of the RRFSO, but I do not think that the CDM regs take 'relevant persons' into account, the regs only really look after the persons within the site. I do not think that the HSE have the slightest interest in enforcing the RRFSO in construction sites, as while people are getting hit by bricks, falling off scaffolding, chopping their fingers off etc, they have much bigger fish to fry.