What Malcolm is saying, is that the conduit itself is already earthed (or dam well should be) and is classed as the circuits CPC. So you will need to extend that conduit CPC by means of a fly lead or the CPC of a multi core cable, to the metal box or BESA box at every point where you have an accessory, be it a lighting fitting, switch, fan, Socket outlet or whatever etc.
Your not earthing the conduit, your extending the earthing (CPC) provided by the conduit to whatever you are connecting to that circuit!!!