You would have freaked out in my old place... I think this kind of setup is so common in London in these flats.
We had a front entrance, and on the right hand side a cupboard with everyones electricity meters, some of which were smart meters.
Next to the electricity meters were also the master sockets stacked next to one another for each flat, then extension wiring fed upto the flats, running side by side to the mains electrical wiring + doorbell wiring for each flat. The BT drop cable came from underground next to all of the electrical wiring, so it seemed even outside the flats these things were mixed underground (although possibly not).
In the flats BT has often installed second master sockets.
It had clearly caused problems as some flats (mine included) had the masters in the cupboard cut out, and the wiring in the walls bypassed. My flat had the original master in the cupboard cut out, and then jelly crimps connecting a new cable, which came out from the cupboard, and then ran along the skirting board, and up 4 floors, following the way you walk - rather than using the cabling built in the walls where the electricals run. Another neighbour also shared my cable, there was a BT junction box mid-way, with 2 cables coming out, 1 for me, 1 for them.
When I had an engineer out he tested my original cable, as it was still there, and stated it didn't pass the noise tests. Interestingly most of the flats were still using that setup.
I went to a neighbours, bearing in mind we were 3 buildings down from the exchange and their TalkTalk ADSL2+ was synced at 3Mbps, they had it plugged into their second master lol. I don't remember the exact NM, but it was around 20db, so it seemed banded. Some of the buildings were EO, others were not, my property had 3 addresses on the BT checker, 1 of which showed fibre so I ordered that and it worked out. My flat had 3 masters dotted around, but only 1 connected and worked.
Honestly you see so many in London with syncs as low as 2Mbps. I go to friends all the time and cannot believe the sync. Probably the worst I've seen is in Canary Wharf they had 0.8Mbps and had apparently had BT out and that was all they could get, due to line length. They also had something called Relish, basically 4G unlimited wireless broadband, but that was equally poor. They were in the TEST socket.
I've also seen plenty of new build with glossy master phone sockets, with built in TV ports. Again the syncs usually poor.
Edited by ukhardy07 (Wed 03-Jan-18 16:33:07)