If identical, then somewhere else the two sets of wires meet and join to the incoming phone line, and you will want to at that point remove one of the 'extensions'

Okay here are the photos of the other socket.

Front of face plate

Rear of face plate

Looks the same to me. Does this tend to confirm what you thought? That they are two daisy chained sockets neither of which is a master socket?

Neither appears to have a capacitor, and neither two cables, one in and one out. There is a master socket somewhere else, otherwisethe circuit will be testing dis.

I'm wondering about the utility cupboard on your floor.

Or a utilitty cupboard in the OP flat ? As we both know the NTE can be in funny places , i have found them in the airing cuboard before now .

It " should " be in the flat but some years back with the so called 3M rule some funny things were done.

Completely agree mucker.

The others are asking about where your master socket may be. The importance of this is that once you are able to find it and gives us pictures of the back of the faceplate, we may be able to help you to another 1.5Mbps or more with a few minutes work from you.

You have to be careful removing the faceplate as all the wires on the back of those two sockets we hope are connected to the removable bit.

Wasn't the 3M rule only for CW1128 external cable coming into the property because of its high flammability?

That shouldn't be a problem here at all. It looks like it's 3 pair CW1308 from the DP here, which I presume is for internal distriibution into the flats. I think there are three flats per 10-pair block - which would be correct for one 3-pair per flat. And they're numbered. This cabling looks new and there are about twenty cables leaving the cabinet.

Are some of the flats still empty? There aren't many lines connected yet.

On the bottom strip on the right you'll see where the cable likely heads out to the master socket by the alarm box - and the emergency lift line too (the darker grey cable is probably labelled 'plant room').

The large multipair cable on the left which terminates on the 10 pair Krone strips is likely to be from the PCP outside.

The other picture here seems to have 3 x 20 pair and 1 x 30 pair cable terminations from various floors. Note that there looks to be a multipair cable in this picture (top left corner) which has been cut. I suspect this is all doing nothing and is left over from when the building was offices with a need for lots more phone lines on each floor.

If each flat gets its service from one of the 3-pair cables then I think it's a bit less likely that there would be master sockets in a centralized location on each floor, otherwise why not run a large multipair up to each floor and break it out there?

The way I usally find out what's going on is to trace the telephone cables with a toner set or cable tracer and see where the cable runs inside and out of the flat. If there's no master socket on that part, it's probably in the utility cupboard.

Just out of curiosity, if there was no master would it theoretically work but poorly - or not at all?

Pass.

No master - phone would work, some very old phones might not ring.

DSL wise no difference, only issue is the star wiring (apparent)