Hi from me too!

[#1]

It might be worth mentioning that if you are disconnecting the phone line to change sockets switch off the router first before unplugging its phone cable. This tells the exchange equipment (DSLAM) that disconnection is at user request and not due to a problem. If it thinks there is a problem it can push up target noise margin (target SNR), which will reduce speeds.
Also disconnecting several times in quick succession is best avoided, and not exceeding 5 times per hour is often suggested as the outside limit.

[#2]

Unfortunately, I cannot do that Oldjim!  My PC is upstairs and the master socket is downstairs in the hall.  My hall has no 3 pin socket to power the computer!  If I contacted the Technical Help people, would they be able to get BT to check out the line?  I tried to reach BT myself a few days ago and after going through all the options found it cut me off because I was not a BT Broadband customer!
Is my own set up indoors partly to blame?  There is a line to my downstairs telephone and another line going upstairs (fitted by BT).  From this, I have a broadband extension cable to my PC.  Were I to move my PC to where the socket enters the room, I would have it close to a radiator - something I remember the techies where I used to work hated!

[#3]

Your internal wiring could easily be the problem and if BT were called out you could get hit with a £150 odd charge.
Is it possible to rig up a temporary extension lead to provide power to the hall.
However, before doing that remove all the phones, Sky boxes etc. and reboot the router - do things change
A further question - what do you mean by a broadband extension cable. Is the router near the socket and the extension cable is from the router to the computer - if that is the case there is no point in moving the computer closer to the router. If you have an extension cable from the router to the socket - how long is it.

[#4]

You will need to do as Jim suggests and test in the master test socket without any extra telephone extension leads sooner or later. If you get a BT engineer he will only test it to the master socket and if he says it is OK there you will get a nasty bill.
If when you test there the router stats are nearly the same we know it's nothing to do with your wiring and extension leads - it cuts down the avenues that need to be explored very considerably.

[#5]

Oh yes, I have a power extension cable which I could use!  I will try later on this evening, have to cook dinner and feed the inner woman right now.  Will be back later!  I guess the broadband extension cable is about 15 ft in length.

[#6]

Quote from: MommaCat

I guess the broadband extension cable is about 15 ft in length.

Is that the cable from the phone socket to the router or the ethernet cable from the router to the PC?
If it is the former that is bad news, if it is the latter and it's CAT 5 cable and less than a couple of hundred metres that's fine. You should always get the router as close to the master socket as possible and then use a long ethernet cable, wireless or homeplug to connect that to your PC.

[#7]

For starters, I am working backwards, and have unplugged the old microfilter (issued by Pipex) and have plugged in the one issued by Plusnet.  I can see there is a difference in the readings.  See what you think of these and if you still feel there is a problem, I will next of all plug the ethernet cable, via the microfilter into the wall socket in here.  Downstairs could be a problem because I cannot open the master socket box.
The extension cable being queried is plugged into the microfilter, which in turn is plugged into the BT socket.  The other end of the extension cable is plugged into the router.
Here are the readings:
DSL Connection
Link Information

Uptime: 0 days, 0:05:26
DSL Type: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 2,880
Data Transferred (Sent/Received) [kB/MB]: 0.00 / 4.56
Output Power (Up/Down) [dBm]: 11.5 / 17.5
Line Attenuation (Up/Down) [dB]: 20.5 / 38.0
SN Margin (Up/Down) [dB]: 21.0 / 15.5
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 11 / 0
Loss of Signal (Local/Remote): 31 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 211 / 0
FEC Errors (Up/Down): 0 / 42
CRC Errors (Up/Down): 0 / 0
HEC Errors (Up/Down): 0 / 0
Using the Plusnet Broadband Speed Checker I am currently getting 2152 Kbps download and 380 kbps upload

[#8]

The results are still rotten - you will need to try the things we suggested

[#9]

The filter to router lead should only be about 6ft long - surely that's not the one you were supplied with the router?
When you say you cannot open the master socket box, why is that? Does it have the removable lower half?

[#10]

No, jelv, I am using a broadband extension cable from the filter to the router.
Thanks everyone for your help so far, but I feel I should leave it for a while and, when my friend is next down, in about a month's time, we can do the check via the master socket together.  I live on my own so it means I have to carry all the equipment downstairs and back up again on my own and do all the setting up alone.  Also, he is more tech savy than me!
I will address the issue again in a month's time!

[#11]

Hello again everyone!  Sorry it's been such a long time but we finally got to moving the PC around on Easter Day!
Whilst waiting for help to do this, I carried out a few checks on my neighbours and my line  with the BT Broadband Speed Checker.  Using my postcode I got an estimated download of 4.5 Mbps.  Using my telephone number I got only 2.5 Mbps.  My next door neighbour's line gave 5.0 Mbps (they do not have a broadband connection) and the neighbours two doors down who have an extension cable to their PC gave 4.5 Mbps.
To explain my own set up, there are two cables running from a splitter box (?) by the front door.  One runs to the downstairs master socket and the other upstairs to a bedroom where I have my PC.  I have run an extension cable from the BT socket to my PC.
Anyway, here are the results from the three tests we ran on Easter Day:
READINGS 12/04/09
In situ with extension cable:
DSL Connection Link Information
Uptime: 11 days, 10:05:51
DSL Type: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 3,776
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 1.00
Output Power (Up/Down) [dBm]: 12.0 / 19.0
Line Attenuation (Up/Down) [dB]: 21.0 / 40.0
SN Margin (Up/Down) [dB]: 21.0 / 12.0
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 1 / 0
FEC Errors (Up/Down): 1 / 277,094
CRC Errors (Up/Down): 1 / 3,836
HEC Errors (Up/Down): 0 / 3,498
Direct from BT Socket in same room:
DSL Connection  Link Information
Uptime: 0 days, 0:01:13
DSL Type: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 3,456
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 18.5
Line Attenuation (Up/Down) [dB]: 20.5 / 40.0
SN Margin (Up/Down) [dB]: 20.0 / 15.0
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 0 / 0
FEC Errors (Up/Down): 0 / 12
CRC Errors (Up/Down): 0 / 0
HEC Errors (Up/Down): 0 / 0
At Master Socket:
DSL Connection Link Information
Uptime: 0 days, 0:02:42
DSL Type: G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]: 448 / 3,328
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 18.0
Line Attenuation (Up/Down) [dB]: 20.5 / 40.0
SN Margin (Up/Down) [dB]: 22.0 / 15.5
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 0 / 0
FEC Errors (Up/Down): 0 / 37
CRC Errors (Up/Down): 0 / 0
HEC Errors (Up/Down): 0 / 0
and a check my friend did with his preferred broadband speed checker:
Broadband  Expert.co.UK
Broadband Expert Speed Test Results: 
Your Download Speed: 3.34 Mbps
PlusNet Average: 2.28mb
Your Upload Speed: 376 Kbps
PlusNet Average: 375kb
What we could not understand was why the bandwidth figures dropped when we plugged into the master socket.  Yes, I have saved the figures in the right order - Keith watched me do it.  I do wonder if the wiring inside my house is at fault.  What do you think?
jim:green post tidied up to make it easier to read mod:end

[#12]

Quote from: MommaCat

To explain my own set up, there are two cables running from a splitter box (?) by the front door.  One runs to the downstairs master socket and the other upstairs to a bedroom where I have my PC.  I have run an extension cable from the BT socket to my PC.

This looks to be a big part of the problem.
Can you take a picture of this splitter box and post (click on Additional Options to add to post) as there is no way a line should be split before the master socket

[#13]

I have photographed it with the cover off - the latter took a bit of doing because it's been there untouched for about 30 years!  Also the postie frightened me half to death pushing a large envelope through the letter box onto the top of me whilst I was doing it.

[#14]

That looks ancient.
To clarify can you give a few words of explanation as it looks at first sight as a simple junction box feeding the master socket.
Is one of the cables the incoming feed to the house and the other to your house sockets or is there another cable I am not seeing
If you remove the lower removable plate from the master socket are there wires attached to it.

[#15]

I have just gone back into it, and nothing seems to be removable.
It is a little box measuring 6 x 4 cms.  The cable you see going into the right hand side of it is the main feed cable into the house.  Exiting from the left are two cables which run parallel to each other across to the staircase, up a few stairs, then one goes through a hole drilled into the stairs and back down into the hall and along to the socket in the centre of the hall.  The other continues upstairs to the socket in the bedroom.