Only way to tell is to take each socket off and see what components are fitted. A master will have a capacitor, resistor and spark gap fitted (at that age of house) however in some cases it may be a 30mm square block with components inside and you will not be able to see it.
Yes, and ADSL filter will work with VDSL/FTTC although the performance may not be ideal and can be on any of the sockets - normally. You will need a filter on every socket where a phone, alarm, Sky box, or similar device is fitted.
It will be interesting to see what wiring is used for the interconnect between the sockets ... it may have an adverse effects if not of a suitable standard.
Once you get in, get some pictures of the back of each socket and we can soon tell what is what and advise on the vest route forward.
M H C
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