What socket do I plug into when told to plug into the "master socket"?

[#1]

gpsmount - I used to work in a factory which made modern telephones for BT, and I can asure you that many phones will not ring without wire 3, and this is most definitely how the system was designed to operate. If someone left it out when they wired your house, your installation is non-standard. (The fact that it works doesn't make it right! :))
There are plenty of old phones about which do conform to the standard, and which do need the bell wire to ring. Their owners have a valid expectation that if they move into a house with telephone wiring, that a standard telephone will work on that wiring. Any "workarounds" to gain better ADSL performance ought to take account of that, otherwise why should anyone ever have regard for "standards"? (The whole point of having Line Jack Units is that anyone can plug any standard instrument into any standard LJU and it will work).
Look here -
http://www.samhallas.co.uk/repository/n_diagrams/5000/N8866.pdf
That's a really old phone, but it's not a dial phone, and it doesn't have a bell in it! Look at the circuit diagram - would it ring on your wiring? This is the way all older phones were wired for Line Jack Unit connections.
I'm sure too that everyone is well aware that there are no "bells" in modern phones - we just use the term generically to refer to bells / buzzers/ ringers / sounders / tone callers - call them what you will!

[#2]

It would ring if you use the correct micro filter.
1) The 4 wire CE marked filter that I have would not work.
2) The Solwise two wire filter would work as it provides the bell capacitor.
3) My broadband was rubbish with the bell wire connected for over a year, and I got no help from my broadband supplier.
4) The microfilter packaging does not state any of this.
5) The DIY sheds do not carry a DIY help leaflet to explain any of this.
6) The house phone extension wiring is my responsibility, and I have to pay for it to be sorted out.
The press is filled with reports about poor broadband service, but I suspect this is a political PR stunt to get an optical local loop for cable telly. See the BBC Fraudband UK on their web site.

I have been told the power plugs are excellent and better than wireless. However at £50 ish they are a lot more expensive than pulling off the bell wire from the master socket.
Well I had to try it out. Consider my wireling as is:
http://www.dougrice.plus.com/Erlangs/adsl_Wire003.gif

I replaced a Solwise two wire micro filter with a the four wire CE marked 4 wire micro filter.
As I have removed the bell wire at the master socket, it is important then the phone plugged directly into the master socket should ring.

If I plug a phone into a 4 wire micro filter plugged into an extension, the phone  should not ring.
So what are the results for my telephones.
I rang home on the mobile:
Converse 300:  
   rings when using master socket via 4 wire microfilter
   does not ring when using extension socket via 4 wire microfilter.

Diverse 4010:  
   rings when using master socket via 4 wire microfilter
   rings when using extension socket via 4 wire microfilter.
BT Decor 310:
   rings when using master socket via 4 wire microfilter
   rings when using extension socket via 4 wire microfilter.
BT Paragon 550:
   rings when using master socket via 4 wire microfilter
   rings when using extension socket via 4 wire microfilter.
Only my old Converse 300 actually requires the Bell wire!

[#3]

"Only my old Converse 300 actually requires the Bell wire!"
..and therin lies the problem! People still own these things, and so for "backwards compatability" reasons, a properly wired telephone system ought to provide ringing voltage on pin 3 of the LJU (or more precisely, on pin 4 of the telephone jack).
It would be nice to do without it, and as you have found, most modern phones don't mind. (I presume they must have their own internal bell capacitor as part of the ringer circuit, which must be connected between pins 2 and 5). The only way to be truly "standards compliant" and eliminate the problems with long bell wires from the master socket, is to wire the entire circuit with only two wires (as you have done) and use filtered master sockets at each position.
(In theory, even this is not quite correct because it lowers the ringing impedance, but in reality, this would only affect someone with enough old phones to take them over REN=4 - and if they were lucky, even this would still ring all phones!)

[#4]

But does this prevent it being suggested with a few caveats!
The plusnet help does not suggest it. I brought a new £40 ADSL modem before I found this out.
Another web page owner suggested that he had emailed the computer magazines and only got a response from one.

[#5]

"But does this prevent it being suggested with a few caveats!
"Absolutely not! And at the end of the day, it's your telephone wiring, and if you are happy with it, that's all that counts!
"The plusnet help does not suggest it" - perhaps understandably though, since they could then be into "my phones don't work since I followed your advice...." etc.!
"Another web page owner suggested that he had emailed the computer magazines and only got a response from one.
" Not a big surprise - I've found over the years that some of the technical contributors in the magazines don't know as much as they'd have you believe. I've come across some technical garbage in the press at times, and when you write in to explain their mistake, they usually ignore you. (Very bad for business if the punters figure out you don't know what you're talking about!)