This may help - http://www.wppltd.demon.co.uk/WPP/Wiring/UK_telephon...
The master socket (a term that if properly used) is the telephone socket that has a capacitor and resistor in it (first pic on the link). All the rest of the sockets should be as pic 2. If more than 1 master socket has been fitted your line will have a lot more capacitance than is required and can suffer from ring trip. Only 3 wires are required to connect extension sockets (the 4th wire shown on connector 4 is not used in domestic wiring but only old business systems that used Earth Recall). As long as you connect every connector 5 (A leg), connector 2 (B leg) and connector 3 (Bell wire), all the sockets will work and ring phones if they are plugged in. Lots of houses were STAR wired with all the extension sockets being wired back to 1 point. The main problem with this method is that the connectors on the back of the face plates are only designed for 2 or a max of 3 wires in the connector.
In this type of wiring you will need an ADSL splitter to connect your router in one socket and the same type of splitter in every socket if you intend to plug a phone in.
If your house has an NTE socket (Pics 3 & 4) this is used as a BT test point. In theory it is connected to the pair of wires coming into your premises with the rest of your house wiring connected to the front face plate. If BT suspect a fault they will ask you to remove the front plate (disconnecting all your internal wiring) and they will then test the line to the NTE. If a fault is found they will repair it but if the fault is on your internal wiring they will charge you or you can get someone else to do it. Thjis type of wiring still requires a splitter in every socket used (as above).
Newer installations have a filtered NTE socket installed. These are similar to above but have 2 sockets on the front plate 1 for a telephone and 1 for your router. No other filters are required in the house for telephones but you can only connect the router into the face plate. (Scoll down on this page to see a filtered socket) - http://www.kitz.co.uk/adsl/socket.htm