Hmm. Definitely sub-standard wiring.
I'll refer to the photographs in the order that you have shown them.
Photos no. 1 & 3. I assume that they are of the same socket? That is an extension socket. Please go back and, referring to no.3, confirm that there are eight individual wires (four coloured pairs, green, blue, orange & brown) & also that the cable outer sheath is black. Is the blue/white stripe connected to IDC2 & the whilte/blue stripe connected to IDC5 ?
Photo no. 2. That is a "700 series" junction box, dating from the period 1959 to 1981. Please unscrew the cover and photograph its interior. Number of wires, colour of wires and what is connected to what is relevant.
Photo no. 4. That is a "master" socket but not an OpenReach (or BT) standard. There is something distinctly wrong in that backing box -- those screw terminal connectors are not OR (BT) standard fitments. Please identify the colour of the cable's outer sheath, the number & colour of individual wires and what is connected to where.
Is there any correlation between where the external cable comes through the wall of the house and to any of those two sockets, one junction box that you have shown us?
Are there any other sockets? Hidden away, perhaps?
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