Sync rate halved overnight on two separate connections!

Bit of long one here for a first post (long time lurker!) but please bear with me - any and all help would be greatly appreciated.

Starting from the beginning....

I have a standard 10(?) core BT cable coming into the house. My wife and I both work mainly from home so, on that cable, we have 2 channels of ISDN (for voice) a domestic analogue line and a second analogue line (BT "Featureline").

Our local exchange is CMDUN - as the crow fly�s we're about 3km away - but about 9km (!!) as the copper runs. So, yes - I know we're never going to get fantastic speeds.

The BT Featureline has ADSL on it with BT Business Broadband and I'm connecting with a Netgear DG834G. When we moved here that was our only connection option and we tended to get about 1 to 1.5MB out of it, not with the best of stability admittedly, but just about good enough.

As of about 12 months ago the 'Domestic' analogue line has an ADSL2+ connection with BE. Sync rate with the supplied "BE box" was about 1.2MB - but with a Netgear DM111P we were getting 2 to 2.5MB - not great, but a darn sight better than the BT line!

So, for the last 12 months, up until yesterday, we've run with the BE connection (via the DM111P) as our primary connection, but keeping the BT connection there as a backup.

Now the fun starts.......

At 14:00 yesterday all was fine - BE connection was quite happily giving a pretty decent speed. I went out for a couple of hours and when I came back at around 16:00 I noticed that the BE connection had dropped and that the DM111P was showing line status as "handshaking". Didn't have the time/energy to look at it then, so just shut the PC down and left it until this morning.

When I started to look at it today the DM111P was still stuck "handshaking". I keep a couple of spare modems (also DM111P's) so I did a complete swapout - modem, filter and all cables - twice. Still the same result though - couldn't sync.

At this point I swapped over to the BT connection, which was up - but very slow only sync'd at 384kbps downstream (448 upstream) - well down on the 1MB I expected. (Admittedly however, as I typically only check this line once or twice a month I can't guarantee that the drop in speed occurred yesterday). I'm currently using this connection and I'm still sync'd at 384 Down/ 448Up with attenuation of 48dB and noise margin of 9dB (downstream).

For the BE connection I resorted to connecting at the test socket. Finally I got a connection - but only at about 1.25MB - about half what I've been seeing until yesterday. Precise stats are 1229kbps downstream sync, attenuation of 53.5dB, noise margin of 6.6dB and Output power of 13.4dBm. Interestingly if I connect to the master socket (but not to the test socket) I can�t sync at all (yes, I know that points to an internal wiring issue but remember that less than 24hrs ago I was getting over 2Mb in a totally different room and nothing has changed internally since then).

BE support, having run some tests, (perhaps not surprisingly) think it�s an internal line issue.

BT (voice) can find no fault.

BT business broadband agree that I�m not getting what I should on the line and are going to investigate � I�m awaiting a call back.

One more point to further muddy the waters� Having talked to both my neighbours, one side (nearer to the exchange than me) noticed their broadband slow dramatically overnight. The other side (further from the exchange) have not been able to connect at all since last night (but were fine the day before).

Given that my master socket is in my kids� playroom (although hidden behind a sofa) I have booked a BT engineer to come tomorrow to replace the master socket, (just in case they somehow managed to damage it � though it looks OK). I don�t think that that�s the problem, but it�s a quick one to rule out and I�m hopeful that I�ll get one of the more helpful engineers�!

Other than that, I suspect that something either at the exchange, or between there and here changed yesterday afternoon and has added one hell of a lot more noise onto the line. Trouble is, I�ve now exhausted my technical knowledge and I don�t know what tests etc I should be asking for / expecting from here on in.

Help me please���..

Could you gather some more evidence from neighbours? It'll make it much easier to pin-point the fault if it is affecting a number of different lines.