I need to add a second socket in the laundry

I have a fair bit of the gib board off so I thought I would try work out where to put the spur so I can run the wires in there ready for the electrician then close up

Theres only one socket.  I thought it would be easy.  I would drop a spur down from it next to where I am putting the machines

However the socket has 3 wires in it already so I assume one is a spur.  It dives off under the concrete floor. I dont know where

What I think are the 2 wires for the circuit both come from/ return to the floor above and I want the new socket lower than the existing

The house was built in 1994.  In the consumer unit there are at least 8 circuits marked simply power

Do you/we have ring mains or ring circuits in NZ or are they all radial?  I know you can spur from a ring main but that you cant spur from an existing spur in a ring main but I think you can spur form a spur on a radial circuit. 

If its radial I think we can tap into the existing spur wire using a new socket put into the existing spur wire and it wont matter if there is one or more spurs further down the line.  If the circuit is a ring circuit I cant do that

Any ideas?

THanks