Cable and
IDC Tool also if you want
Cable clips though you could probably get a smaller quantity at a good ironmonger.
Personally I'd get enough cable to do the whole lot. Do your extension & also lay the cable in place from the box in the loft to the master. Then if you feel confident, do it yourself, otherwise very little for a BT man to do, just make the connections.
The cable is twisted pair which is why it's not vulnerable to interference in the way the old cable is. This one is 2-pair. There is 3-pair, but you only need 1 pair, so 2-pair is fine.
The Pair to use is the Blue+white trace and the White+blue trace. From master to extension the Blue+white trace goes to terminal 2 and the White+blue trace goes on terminal 5. The bell wire you don't use in a Broadband situation, it unbalances the pair and acts like an aerial, otherwise the Orange/white would have gone on 3. You'd use it if you had central filtering, but with plug-in filters they generate their own locally for a phone.
From the box in the loft, the Blue/white would connect to the terminal that has the White incoming (B-wire) and probably has a solid blue colour on it atm. The White/blue trace would go on the terminal with the orange incoming (A-wire) and probably has the orange solid colour on it atm.
At the back of the master, the Blue/white goes to B, and the White/blue to A.
You do not strip the wire, it's pushed down into the IDC (Insulation Displacement Connector) terminal with the tool - never use a screwdriver or similar as it would force the jaws of the terminal open making a bad connection. Old wires you just pull vertically out of the terminal.
HTH, ask away if I've missed something or you aren't sure of something.
