So turns out the alarm cable issue goes little deeper than my phone extension wire. Had one of the original electricians over today and he admitted they had messed up and used alarm wire to connect each apartment's master socket to the communal cupboard hub where the lines reach the building from outside.
Basically, my choice is now to either leave it as is (tbh, it's pretty fast and seems reliable) or get a BT engineer to re cable my apartment's connection to the communal cupboard and go along surface of my hallway wall to the socket or even just put new master socket by front doorway. Not sure it's worth it for what I suspect will be a 5-8mb speed increase on download. Upload is already max (20mb).
Basically, my choice is now to either leave it as is (tbh, it's pretty fast and seems reliable) or get a BT engineer to re cable my apartment's connection to the communal cupboard and go along surface of my hallway wall to the socket or even just put new master socket by front doorway. Not sure it's worth it for what I suspect will be a 5-8mb speed increase on download. Upload is already max (20mb).