You should have atleast 4 cores in the cable connecting to the master socket:
blue with white bands, orange with white bands, white with blue bands and white with orange bands...
A master socket only needs 2 of these cores, the blue with white and the white with blue.
To connect a slave to a master you need the orange cores aswell.
Locate the main box where the cable enters your property and see what the cores look like. Usually there are just 2 entering your property into a box, this is then connected to the master socket with 4 core cable (of which only 2 are used, the other 2 may have been cut back to the sleeving or connected for the hell of it.
You really shouldn't mess with the master socket as its BT's property - much like the electric meter and main fuse is the DNO's property. But if you want to go ahead anyway atleast you won't be killing anyone if you make a mistake and there isn't a metal tag and label warning you not to touch.
Ultimately, if you have plenty of 4 core cable (about £10 for 100m from
screwfix and a cheapo IDC tool) then you can just connect them all yourself.
1 = Not used
2 = Blue with white bands
3 = Orange with white bands
4 = White with orange bands
5 = White with blue bands
6 = Not used
Hope this is of some help.
Davy