My bungalow has an old fashioned telephone system consisting of a BT
cable connected to a grey box (about 70x40mm tapered with a single
screw fixing). From here there is a wire to another identical-looking
box - only two core of the wire are connected). From this second box
there are two wires going to BT/RJ-11 sockets (65mm square surface
mounted bearing the old 'T' BT logo) - there are six wires connected in
at least one of these - there are three boxes and the interbox wiring
is not easy to trace in the loft. I have ADSL filters on all the used
sockets, of course.

Now I'm about to modernise everything, and it's a convenient time to
replace this wiring.

1) Can I install a modern Master Box directly from the first grey box?

No. BT have to do it. If there is a disabled person living in the house you
may be able to get it done free of charge. Details here

http://www.bt.com/customerservices/c...econv_phsocket


Or do I have to pay BT to do this? (I'm aware that there is moderate
voltage (-48V ?) on the wires!)

See above.

2) Can I then wire new extensions from the master to ADSL-filtered
wall sockets throughout? I'll want 5-6 sockets, although I don't
foresee that many instruments - probably: Sky-box, ADSL modem,
Speaker-Phone and DECT-basestation (REN 4).

The best way to do it is by wiring from a replacement front panel for the BT
box.

Lots of informaion at http://www.clarity.it/acatalog/telecoms.html

Peter Crosland