Questions regarding my current set up during an ongoing fault

[#1]

I've been dealing with the support people regarding some speed issues-deteriorated over the past couple of weeks till I was only achieving 0.7mbs.  Anyway a BT engineer was on the phone today and I'm up to 3.1.  Hoping the fault diagnosis continues because I used to achieve 6.5-presumably it will since no one has said the fault is now clear.
Anyway since Friday, I have moved my router, so it's not using an extension cable.  I have put the following on several tickets but no one has answered yet, so I thought I'd try here.
Could you please answer the question at the bottom of this message?
BT main socket is open
ASDL filter is in the test socker(as per video you sent)
modem cable is in the filter's dsl socket and connected to the router directly ie no extensions
main telephone is in the ASDL filer's telephone socket
However this leaves my Sky box and bedroom extension not connected.
QUESTION
Can I plug my original extension/doubler into the phone socket of the ASDL filter so my sky box and bedroom are connected or would this nulify the test?
(Note I'm physically disabled and work from home.  It's a pain no longer having a telephone on my own residential line in my bedroom where I work but yes I do have access to lines owned by my employers).

[#2]

Can you describe how everything was set up before Friday please as that may explain the problems you were having.
Is the extension to the bedroom connected to the back of the master socket, or was it connected via a doubler in to the front of the master socket?
I suspect it was the latter from what you have said. If so, was the doubler plugged in to the master socket with the filter plugged in to the doubler, or was the filter plugged in to the master socket with the doubler then plugged in to the filter.
Have you got another filters and if so where were they fitted?
Where does your router need to be, can it be by the master socket? This is preferable as it will give the best speeds, but with care it can be sited elsewhere. If you need the internet connection elsewhere, could you use a long ethernet CAT 5e cable between the router and PC? This would not cause speed drops.
I won't be about again until tomorrow evening, but if you answer these questions there's other around who will be able to point you in the right direction.

[#3]

Quote

Can I plug my original extension/doubler into the phone socket of the ASDL filter so my sky box and bedroom are connected or would this nulify the test?

It's definitely worth seeing if the speed increases while this is unplugged as extension cords can be a big cause of poor download speeds.
As Jelv says, if you can give some more info about how your router is setup then we'll be able to give some more advice.

[#4]

I wanted to keep it brief and therefore didn't give full details.  I'll ask my question again, hopefully more specific, then try and give you full details.
I have temporarily disconnected my bedroom extension, while I have my main phone and broadband plugged into the filter, which is directly plugged into the BT test socket (As requested by plus net support).
Please note I had no problems until several weeks ago.  Went over my download limit and was throttled down to 128k, during peak hours.  I also noticed that I was getting about 3.5mbps outwith peak hours-which I felt was strange, since it was neither the throttled speed or the speed I'd been used to for several years of 6.5mbps-I'm about 0.5 kilometres from my exchange.  I decided to go to unlimited and asked to be transferred to this package before the invoice date.  This was done but I only achieved 3.5 which reduced during last week until 0.7.
MY SET UP BEFORE LAST FRIDAY
(I would like to emphasise that the set up described below, has not changed since I activated broadband in 2005).
There was a double adaptor extension plugged into my main socket.  I need to clarify this-I did not say double adaptor-since as well as the 2 sockets, it has a wire going to a DIY junction box which feeds the extension into my bedroom.  In 1 of the double sockets is plugged my main telephone (obviously via an asdl filter).  In the other socket, there is an extension to behind my computer desk.  Now presumably this extension has a doubler, since my sky box is plugged into a cable that leads behind the computer desk.  My router was plugged into presumably the double socket behind my computer desk.
Unfortunately between the heaviness of the desk and the amount of equipment, I am not able to double check, but my description above must be correct.
Now as I type this, I'm thinking not the best set up (understatement!).each time I examine it, I wonder whether it's time to redo the extensions however that would be a job I could not physically accomplish owing to my disability.
HOWEVER I should state that the above set up was in place before I bought broadband in summer 2005.  In other words nothing has changed  since then to explain the speed drop in the past 2-3 weeks.
SINCE FRIDAY AROUND 11 PM
Moved my router so it's now plugged directly into the BT socket (opened socket at the request of plus net).  Therefore from the open BT socket there is an filter which has my router and main telephone plugged in-therefore no bedroom or sky.
Note when I initially moved my router, for a couple of hours, I had zero dsl signal.  I think it was this that convinced plus net to escalate the problem to BT.  So for about 1 week now, I've only been achieving speeds of.7 (note before and after moving the router etc).  A BT engineer telephoned this morning and by lunch time I was achieving speeds of 3.1mbps.  Better than.7 but still less than the 6.5 I used to achieve.  My ticket has not been updated therefore I'm assuming that BT have improved it but are not finished it.

Yes I have questions for the future-do I keep the router behind the TV so it's plugged into the main socket without an extension.  However, I'll deal with stuff like that once my speed is sorted out.
Meanwhile, can I, as a temporary measure, plug the doubler extension into the filter, which is plugged into the test socket, so I can use my bedroom and sky or is this adding variables that we don't want while my speed fault is being investigated.
(Yes there is also a cordless handset in the living room, which my mother can use, but I cannot owing to how I grip the phone)
hope this makes sense!

[#5]

Should have added there are/were filters on all non broadband equiptment.

[#6]

After all the testing is done you should put a filter directly into the BT socket and you can then run all your non-ADSL equipment through this single filter (doublers fitted after the filter).
Things like double adaptors ought to be OK - but might not.
It is possible for all this internal wiring to pick up noise, which it will feed into your router - you can buy things like special faceplates for your BT socket which can help a lot.

[#7]

On a point of clarification, I think you need to say whether these speeds to which you refer are "throughput" speeds by using some form of speedtester eg. http://www.mybroadbandspeed.co.uk/ or whether they are the sync speeds from your modem/router.
If it is throughput speeds, then forget them for a moment, it is the sync speed stability that needs to be established first. If your line is stable then throughput speeds are a totatally different issue.
Your sync speed determines your profile which determines the maximum throughput that you could achieve. The actual throughput is not only determined by this profile, but exchange congestion and any traffic shaping & throttling that may be applied by the ISP.

[#8]

What you need to do is to record the stats reported by your router (sync speed, attenuation and noise margin) while you are using the test socket with minimal other equipment. This page tells you how to find that data for many common routers; if you can't find what is needed post back the make and model and hopefully someone will be able to help.
Having done put the front back on the master socket and plug the filter in to the front of the master socket with everything else as you have now. Compare the stats, if they are worse (downstream sync speed or noise margin lower) we need to investigate.
Having done that, plug the doubler extension in to the filter with all other equipment (Sky box etc.) disconnected - check the stats again.
Now plug in each of the other cables/equipment one at a time while monitoring the stats to make sure nothing causes a problem.
If you have trouble interpreting the stats just post them here and we will help interpret them.
Long term I would recommend a filtered face plate to replace the face plate on the master socket. This will give you a ADSL socket in to which you can plug your router directly and a phone socket in to which you can plug your doubler extension and everything else. Nothing plugged in to the phone socket would need to be filtered.