Since I posted my original question I did a bit of googling and it confirmed that all it does is disable the bell wire which is now redundant.
Pulled out all the orange and yellows from pin 3 and hey ho...all my extension sockets run at only a slightly lower speed than my master test socket. (Have had to have router plugged into that for ages in order to keep connection, my master socket is through the bathroom in the boiler room which needs a rabbit-run power supply for the router to work.
I'm quite chuffed
Early days though...
Edit: Thanks B,Fraser