CW1308 cable, and typically 3 pair. You only need worry about using one pair of this cable and the other two pairs are coiled neatly in the back box for possible future use.
RIC - You are very miss-informed.
There is a SINGLE pair (2 cores) from the exchange to your home (master socket), and then this single pair travels around your home on 2/5 to provide the line. Terminal 3 is also required from the master socket to every secondary (not slave!) point. This provides the ring current for the bell/tweet tweet in the phones on secondary points.
2/5 must always be a 'pair' - these are denoted by the colour markings - blue/white and white/blue for example. The pairs are gently twisted together through the entire run, and as such, any interfence generated in one leg is cancelled out by the other leg as the two legs are not in 'phase' with each other.
When using multi-pair cable, the blues are always pair 1, oranges pair 2, greens pair 3, browns pair 4, greys pair 5 - after this the 'base colour' alters from white to red, and the sequece of bl, or, gr, br, gr starts again. For more than 10 pairs, the base colour is then black and then yellow (upto 20 pair).