Thanks - but more questions! (Sorry)
2 cores from BT come into the NTE5
connect them to a and b in the base of the NTE5

Yep - 2 core from BT into back plate of NTE5 digital access adaptor
plate, screwed into A and B. Note that these wires i have connected to
A and B are green and green+white. I presume i leave the rest of BT
core's wires i.e. orange, orange+white, blue, blue+white alone and
dangling?

On the frontplate of the NTE5 connect from a to ca and b to cb

So you mean connect the A of the IDC to CA of the SAME IDC?? why do i
need to do this? Same for B-CB. What about CS well?

Connect all extensions to 2345 on the NTE5 frontplate

OK - so can I use the BT core's blue and blue+white to connect to 2 and
5 and then connect the other end to my other bt extension sockets??

Sorry to be a muppet on this but the way my cable has been done just
doesn't look like what I'm used e.g. me dad's place or my mates who
only has 1 master socket.

If the second socket next to your NTE5 is a master then you ought to
convert it to a secondary

i think it used to be - as there is a capcitor and other stuff i only
find on master socket normally...

OR just get a new NTE5, and wire it in the conventional manner (you
can then miss the bit about a-ca and b-cb loops)

hmmm - am i going to get into trouble by replacing the current NTE5 as
this to me seems like acting as the "master" now?

thank