Just to follow up, are you sure it isn't one of these that you have? If so, that's an Interstitial plate (and it is removable via a slot). If it's a modern one you'll see two connections (called IDCs) on the Interstitial plate. What you have to then do is find out which is the wire for your chosen extension and take the two signal wires (it will be the blue and white/blue and connected to these IDCs on the faceplate). You need an IDC tool to do that (very cheap and easily available), although it is possible to do it with a thin bladed screwdriver. (They are called IDCs as it stands for "Insulation Displacement Connector). Basically a sharp metal slot that pierces the insulation and connects with the copper underneath.
I'm fairly convinced from your description that this is what you have.
Note that you may have a single extension wire and the extension sockets are simply daisy-chained (that is the wire goes to the first socket then onto the second). In that case, you might as well just run without the Interstitial socket as you'll gain nothing from what I describe. It will not be optimal though, and to do the job thoroughly you'd need to run a separate data extension wire from the Interstitial plate. Using CW1308 cable.
Note that if you do remove the Interstitial plate, you will need microfilters on any socket where you plug phones in.
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This may also be of help as it's got a picture with a red circle round the Interstitial's unfiltered output
But bear in mind my other points. If all your extensions are just daisy-chained off using one extension cable, then it's pointless moving that to the Interstitial plate. You might as well run without it unless prepared to rejig the extension wiring.
Edited by TheEulerID (Sun 10-Jan-16 19:33:18)