Is this slow BB caused by 40-yr-old wiring?

Please could you TBB experts help me to help our friends whose BT BB has slowed to a crawl in recent months? TBB speed check gives 0.34Mbps and they have the odd crackle on their phone line.

The house is 45 yrs old and they believe the wiring is original. An armoured underground cable emerges below the garage wall and enters a circular junction box marked BT NO 18SSA GPO. The contacts therein are corroded and there is much insect debris. The underground cable carries four conductors, green and black being unused, blue and orange entering a four-core grey cable which I have seen normally used for interiors. This cable's outer plastic sheathing is broken in many places, exposing the core conductors, as it runs along the outside of the garage and through the eaves into the roof space.

Somewhere up there must be a junction as one cable re-emerges to run around the outside of the house before going through a window frame to feed a phone extension. The Home Hub is plugged into another extension socket in the office. These sockets are both extension type about 85mm square; there is no BT master socket in the house.

The HH stats are: Line state down 283Kbps, up 888.
VPI 0/38
Modulation ITU-T G.992.5 Interleaved
Noise margin 15.1/13.8dB
Line attenuation 35.5/19dB
Output power 0.0/12.8dBm
Loss of framing (local) 0 Signal 0 Power 0
FEC errors 116/4294967228

Am I correct in thinking the poor wiring is to blame for this? I think it would be best to call BT and have their engineer renew wiring from the round socket to the office, fit a new master socket, and scrap the existing tangle. My friends are happy to pay for this if necessary once they had seen the state of the box and wiring.

It surely cannot be helping.

Just out of interest: would the BT NO 18SSA GPO box be the demarcation point in this case?

Isn't the demarcation point always a socket, not a junction box?

I agree that the grey cable can't be helping - especially if the cores are exposed. There might be other faults with the line, but you'll never be able to tell until that section is ruled out.

In reply to a post by WWWombat:

Isn't the demarcation point always a socket, not a junction box?

I was just curious since in this case there are two extension sockets linked to perhaps another junction in the roof space and the OP says there doesn't appear to be a NTE5 in the house

No, that's the equivalent of a BT66. Most likely, there is no demarcation point, since it ought to be the first point on the feed where the external cable comes in.

In reply to a post by Malwaremike:

Am I correct in thinking the poor wiring is to blame for this? I think it would be best to call BT and have their engineer renew wiring from the round socket to the office, fit a new master socket, and scrap the existing tangle. My friends are happy to pay for this if necessary once they had seen the state of the box and wiring.

As Zarjaz says, the wiring can't be helping. Some photos would be fun.

In reply to a post by Zarjaz:

No, that's the equivalent of a BT66. Most likely, there is no demarcation point, since it ought to be the first point on the feed where the external cable comes in.

Definitely a job for OR then: new cable from the BT NO 18SSA GPO (and possibly even replace that?) to a NTE5 in the office. Then the extension could be wired from the NTE5 to the other room by anybody...

Cut back on the UG feed also, get rid of the breaks in insulation on the incoming pair, loose the current corroded terminals in the bakelite box. New feed to a single NTE where required, jobs a good 'un.

Might (?) get the job done for free since the OP said there 's the "odd crackle" on voice