Noise Margin

[#1]

OK, so here's the downstairs extension:
There's a brown wire which has either been disconnected or worked its way loose - do I need to connect it?
Otherwise, connections are as follows:
2-blue
3-green
5-orange

[#2]

The brown wire is unused. OK, unfortunate that it is this socket that has the old standard wiring which you will need to replace with the correct standard CW1308 cable. It's a fairly straight forward cheap DIY job if you don't mind removing the old wire and clips and fitting new. If so, I'll give you a link for what to get!
By the way I assume the correct standard cable going to the upstairs socket probably goes behind  that vertical trim?

[#3]

I don't mind tackling the job, only since the existing wiring goes under carpet and through walls I won't be able to follow the same path and things will look somewhat more unsightly >:(.  However, if it has to be it has to be...
edit: no, the upstairs wiring does not go behind the vertical trim.  It's one of the cables protruding from the right hand side of the Master socket.  It may look like a single cable from the photo but there are two there.  The cable goes down the wall and under the stair carpet, where it then goes up (under the stairs) to the upstairs room where the socket is.  It's an old Victorian house so everything was put in after it was built!

[#4]

And here is the upstairs socket.  Looks completely different.  It's a neater looking job but different coloured wires:
2 - blue (with white dashes)
3 - red (with white dashes)
5 - white (with blue dashes)

[#5]

This is not going to be easy but if you want to get rid of the star wiring you would need to run a new wire from the one upstairs to the one downstairs - is that even remotely feasible

[#6]

Jim, star wiring isn't an issue as long as it's all the correct standard  but if it's an easier cable run from upstairs to the socket where the modem/router needs to go, then fine.
Modern CW1308 is a bit smaller and neater. These CableClips and a Disposable IDC tool to make the connections should see you right. The firm in the links is a reputable company and the P&P is quite reasonable compared to some (no,I don't work for them!). You need to be careful where you buy the cable as there is fake CW1308 about.
You may find a local Telecom/Hardware shop that has the items, but I doubt they will equal the price and you need to be sure they got their cable from a reputable source - not any old supplier off an auction site

[#7]

if I understand you correctly, you're talking about connecting the downstairs extension to the upstairs one, not re-wiring between the upstairs one and the master socket?
edit:  if so, do I then disconnect the wiring between the downstairs one and the Master socket?

[#8]

That's correct , the cable to upstairs is the correct standard and doesn't need replacing. Yes you can connect from upstairs to downstairs if it's an easier run, if not use the existing run from the Master (or new route if more convenient). Yes, you end up disconnecting the old cable altogether.
The new cable mentioned in my previous post is a 2-pair cable, all that's required for an ADSL installation. The newer cable you have going upstairs is 3-pair and has unused wires. When you do the wiring your need to remove the wires from Terminal 3 by gently pulling them vertically out of the terminal. The only wires that will be connected are the Blue+white trace to terminal 2  and the White+blue trace to terminal 5 at all of the sockets.

[#9]

Thanks.  Re-routing downstairs looks like being more practical, but I'll have to put my thinking cap on as to the best way to do it.
If I go ahead and re-cable then would AndyH's suggestion of putting in a new NTE5 be advisable while I'm messing about with the wiring anyway?  If so that would mean no more ADSL filters needed I guess?  Or would it provide no practical benefit?

[#10]

No practical benefit, his suggestion referred to a Filtered plate. The usual "benefit" of a filtered plate is if it is convenient to plug your modem/router in at the master and you have several extensions used for phone only, then you wouldn't need filters in the phone locations as it's done centrally (at the NTE) but you can never run a modem/router from those extensions because they are filtered for phone only.
If you want to run a modem/router at an extension in that situation you have to have a separate cable pair from unfiltered terminals on the front plate to the dedicated extension (not all filtered front plates have them).
In your case with just 2 sockets, it's no advantage whatsoever and in any event you only need the 2 filters you have already got.

[#11]

ah, OK, not for me then, thanks.
On another note, I'm happy to take the plunge and redo the wiring but the results of tests I just carried out indicate that I still have a problem elsewhere.  

If I'm getting this while connected to the test socket then doesn't that indicate I may have a problem on BT's side of things?
I'm also getting packet loss showing up on my TBB graph, which is odd as I haven't had that for several days (i.e. pre-test socket).  Another thread seemed to indicate this was cause to raise a line fault.  Is that the case here?
edit: in case it's not obvious, master socket is no longer valid which is why it's now showing up as constant packet loss.  I'm referring to the bit before that
edit: I think it's because I was on the dreaded pcl gateway.  Just rebooted and I'm on ptn - will see how that goes

[#12]

OK, I've ordered the items as suggested by Anotherone and will re-cable the downstairs socket when it comes.  If you don't here from me again it will mean that I've been none too delicate and ripped out the wrong wires in the process, thereby cutting me off from the telecoms world ;D.
Question: now that things have settled a bit (i.e. got my Skype back :)) and I seem to be on a stable gateway, would it be worth switching interleaving off again?  I think Jelv mentioned above that with me being so close to the exchange it shouldn't really be necessary.  I'm hoping that might help the latency on the gaming side

[#13]

There's always the Test socket 
I wouldn't worry too much about that awful pingtest yesterday evening, as it was at a peak time and some of the problem may have been Ping Server related. If you get repeated results like that, especially at non-peak times then that would be something that needs looking at.
Useful checks are to run ping ntp.plus.net from a cmd prompt (Plusnet's DNS servers) so staying within the Plusnet Network, and if this shows repeated problems do a tracert ntp.plus.net to see if it identifies a particular Plusnet router.
If you could post another RouterStats summery page (as per reply #32 - but without your current IP address!) and assuming the errors look Ok then you could respond to your open fault ticket and ask for Interleaving to be turned off.

[#14]

Thanks.
The thing about the pings is that I got much worse ones when connected to gateways other than at Telehouse North.  Don't understand why.  Also, for reasons I again don't understand, I was suffering much more packet loss with different gateways.  Oddly enough, according to TBB I suffered less (i.e. zero) packet loss when connected to the Master socket than I do now (very small amounts) connected to the Test socket, even though I am a similar gateway (ptn) than before.  Despite this, however, the connection "feels" better as I'm finally getting my Skype to work and gaming also seems to run smoother (scratches head).  Witchcraft, I tell you.
Attached the stats.  Couldn't get rid if the displayed IP address even when unchecking boxes in the settings so resorted to trusty Paint program

[#15]

Paint does come in handy, odd about the check boxes. Pings do vary a bit from Gateway to Gateway even in the same Telehouse, so I wouldn't worry too much about that.
I had to put put my glasses on and get a magnifying glass out to look at the error figures 
I should respond to your ticket stating that you discovered you have some wiring issues and are going to remain in the test socket until they are resolved and that as the line now appears to be pretty much error free will they please turn Interleaving Off (not Auto - Off).