I am afraid that the previous answer was incorrect. It is actually illegal to do as suggested. The Slave Sockets MUST be wired from the BT Master socket.
If you intend to use Broadband here are some tips. If you can, plug your router into the Master socket. It is is a modern (NTE5) socket (You can tell by undoing the two screws. It is has another socket underneath then it is an NTE5.) then it is even better to use a filtered faceplate. Which will mean that you won't need micro filters on the slave socket(s).
If you intend to plug your outer into the slave socket then connect ONLY the following wires to the slave: Blue & White to 2 and White & Blue to 5. DO NOT connect any other wires they are nopt need and can screw up your Broadband.
t
December 2007