not Al Cu here
Chances are you are not even on copper, for a period in the late 70s/early 80s BT was repairing/re-routing telephone connections with an AlCu alloy that was "good-enough" for voice, due to copper prices The problem is no-one kept track of exactly where it wwas deployed, and its some of the trunk cables too, so BT won't pull up and replace it, even when they find it....
the problem is the profile on the line needs to be tweaked a lot to get a decent speed, and it depends on where in the line and how long the Al sections are...
Biting the hand that feeds IT
