We do the same as you. A qualified spark fits an RCD to an existing socket in the room and we then come off that for further sockets if required. As far as I know we only check the earthing of the existing sockets.
See below for response to recent email from Gerry Boyle on the subject:
1. Electrical supply
i. What do we test for?
we check for earth continuity, the correct type of cable as been installed to the socket we will be using, visual check of the house fuse board and rectify minor problems ie blanking plates missing from live ways in fuse boards.
ii. Who tests?
Qualified Registered Contractor
iii. How often do we re-test?
iv. Do we monitor usage?
No but we do reimburse the patient.