None of the pictures show a master socket - why?
A master socket should have something connected to terminal points A and B, and then an extension (or more than one extension) running of of different pins 2 and 5 (maybe with an orange on pin 3).
The key is seeing what is under the cover at http://www.flickr.com/photos/[email protected]/5565147764...
From what one can see it looks like a grey cable enters the property, and this goes to a socket, which also has an extension running off the same IDC terminals to the extensions, i.e. you have a daisy chain configuration, with no actual master socket.
Whether this is causing you problems impossible to say without removing the daisy chain and just testing with minimal wiring present. The Annex L is unusual and not sure it is approved for UK use or not - so rare to see it, first time I've seen it.
I would recommend finding a router among your collection that lets you force the various ADSL modes and find a G992.1 Annex A ADSL over Pots mode.
Also if it were my property and in this state, I would be getting an NTE5 master socket and fitting it and tidying up the wiring too.