Two lines in use, one master socket that is bypass...

Question

I work at an organisation that has a subscription for two lines. One line is used for the main phone system of the business and the other is used for two purposes: 1. There is a payphone for guests on it; 2. The business internet connection comes through it (DSL). The internet connection is noticably slower than it should be and often drops out, so I've had a look at the wiring of the phone lines.
Both lines come into the building from the pole through a single 4-core black drop-cable, as is quite normal I think. This cable comes into the back of an NTE5 master socket. The wire colours are Green, White, Orange and Black. None of these connect to any part of the master socket - neither the main panel, nor the removable front plate. Instead, they are all connected with the little translucent crimp-type things to the wires of the internal "extension" cables. My first quesion is, is this correct? I think it's incorrect, especially as one pair of wires immediately gets split off to 2 extensions, as I'll now describe...
From the master socket there are two "extension" cables. One goes directly to what I think is a normal extension socket (smaller than an NTE5, but it does have some kind of inductor or capacitor, and it looks modern). This socket's pins 2 and 5 are wired directly from the orange and white wires respectively in the drop wire. To this socket, the ADSL modem is connected and nothing else.
The other extension cable goes off somewhere else. However, it must be carrying two phone lines - because the payphone must come off it (which shares the line with the modem), as must the main phone system. It is a 6-core round white cable. Its Orange and White/orange wires are connected to White and Orange in the drop cable (i.e. the same pair that goes to the modem extension) and its Green and White/green wires are connected to Green and Black in the drop-cable. I haven't been able to trace this cable yet, but all I know is that it must end up splitting off to the pay phone and the main phone system, because they are separate lines.
So, is the incoming line not terminated correctly, in that it doesn't connect at all to the master socket and the one pair of wires immediately splits off to two extensions? Could this be causing the internet connection problems?
Any help would be greatly appreciated - preferably from one of you former BT men ;-) I'm trained in electronics myself, so answer technically if you want.

Answer 1

Yes, the payphone has a filter.
Yes I agree that the line the main phone system comes off may not need a master socket for whatever reason (i.e. it may have its own circuitry).
But as for the broadband line - it splits off to the payphone extension and to the modem extension as soon as it leaves the drop wire, which seems wrong to me. As far as I understand, one of the purposes of the master socket is to be able to detach the front plate in order to isolate the consumer's extensions from BT's line; but with the extensions being hard-wired in, that's imposisble. And with no master socket, I assume that whatever circuitry is normally in a master socket isn't present on the line. Does this matter? Is it just surge protection, or is there some kind of filtering as well? We will of course contact BT about this, but I'd like to know first whether there really is something wrong.