When you say bus do you mean one of these in a small plastic enclosure? Connect large cable from rod and small cables from outlet and fridge follow?

No.  I mean a wire.  Since you will have RCD, the wire just needs to be size to handle the "buzz" that you might get from a computer or stove.  IE: less than 30 ma.  So, you could go with 2.5mm2 - just need to protect for physical damage and best to put under conduit.  By "bus" I mean that you don't need to make separate runs from all the places you want to have ground.  Just connect to the bus which is connected to your rod and/or CU.