Many thanks for your input and my apologies for the silence, I tend to travel a lot for work and don't get much time here.
In response to some of the questions earlier:
Banger - telephone provider?
* Origin Broadband ADSL 2 I assume, as I saw the line sync speed regrade several times in the first few days.
Apparently the property is linked to an FTTC exchange, which is oversubscribed and not accepting new orders...
Zarjaz - Will Origin not raise an SFI fault for Openreach to attend ?
* Based on the other responses, I'm still not clear whether the wiring is considered mine or belonging to Openreach and am nervous about poking around where I'm not 100% clear if it's my responsibility
RobertoS - External NTE?
*On the Outside wall a few feet away from the supposed master socket there is this box - is this an extnernal NTE?:
I couldn't locate any other sockets inside the property that could be a master socket, although I did find an additional extension socket on the top floor. There is no overhead cabling in the estate so I'm positive I've already been dealing with the 1st socket inside the property
Regarding the orange middle cable, would this be as simple as carefully removing the twined orange cables, separating the two and then replace one at a time and checking the line stats (making sure not to touch the blue and blue/white)? Or can the orange cables be simply removed and not reconnected?
For additional info, these are the line stats reported by the router at the moment: