Stephen wrote:
I fitted an extension socket and was reading which colour cable to
connect where. I was using wires with two pairs: blue/white and
orange/white pairs. I read that rarely a third pair (green/white) is
connected to terminals one and six. What were these used for and why
are they no longer used? I am guessing they were used for something
once upon a time otherwise they would not be there.

I believe that terminals 1 & 6 were for Telex.

See Table 1 of SIN 331, "BT 50 Baud Telex Service, Interface Description
& Withdrawal Notification", http://www.sinet.bt.com/331v2p1.pdf

You should be able to find the specs for pretty much anything related to
BT services on http://www.sinet.bt.com/

Rich.