SNR is 3.0dB !? Frequent disconnections in the evenings too.

[#1]

Yes BT own everything up to master socket and the inner part of the master socket.
Had a BT engineer around my house the other day to fix a problem I am having and I asked him about this, for the next 15 mins he told me of stories of woe about persons who had messed with BT wiring and made his life harder =p

[#2]

Ten-day retraining period over, with no particular change to the reliability of the connection (ie rock solid during the day, very flaky in the evenings).
However, something odd just happened - two (voice) phone calls this afternoon during which crackling was heard on the line. Simultaneously the SNR, which has been 5.5 all day, went beserk and is now running at 11.5, which I've never seen before.
Probably a proper line fault?
Routerstats graphs attached
Phil
EDIT: Both the crackly phone calls were from a number on the local exchange. Calls from mobiles & other exchanges haven't been crackly.
FURTHER EDIT: While my sync speed dropped to 1568Kbps when the SNR went up to 11dB, the connection has at least remained entirely stable all evening, which is a first.