Hmm . . . A very, er, interesting set-up.
Just to confirm that I understand correctly, your
first picture is the rear of the
RJ45 socket that is labelled (what looks like) "D7/10A"?
I don't suppose you know from where that purple Cat5e cable originates? There must be a multi-pair
Openreach service cable entering the building, which should be terminated at a distribution point. Hopefully that purple cable comes directly from the distribution point.
Perhaps you should ask your Management Company to show you where the
Openreach service cable enters the building. (Remember to take your camera with you.)
I am surprised at what the installing
Openreach engineer has done within your flat. It certainly is rather novel.
To be perfectly honest, overall, I do not think there is much else you can do.
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100% Linux and, previously, Unix.