It's a long time since I've taught about ring mains. In essence, the live and neutral wires both form loops from the box going back to the box. Appliances are then connected between live and neutral. This means that the appliances are in parallel and thus independent of one another. The mark schemes used to point out that as current could flow either way out along the live wire to the appliance, only half as much current went through any one wire so the wires could be thinner.
