Regardings your advice on ring circuits, the maximum floor area allowable underBS7671 is 100 sq. metres not 120. What must be taken into account is the fact that the maximum lentgh of the ring (to the last outlet and back to the board) using 2.5mm cable must not exceed 66 metres. Remembering that all sockets on an earth rod system and sockets on ground level on a PME system must be protected by a RCD.