Depending on the age of the property , that looks pretty ‘standard’ for housing build in the 1960’s through to late 1970’s , it’s common to have an underground cable to an external block ( the grey BT 66 block ) and cables to an interior ‘decor’ socket , that was part of the developers interior design specification , to give a modern finish ( what was modern in the 1960’s ) , so although the socket in the image is not an NTE5 type master , it is the main socket .
It was also common to have extensions wired from the external block , that’s bad from both from a ADSL performance point of view , and also doesn’t allow easy disconnection of extensions, as can be done with NTE5 type sockets , which became ‘standard’ in the 1980’s , but when telephony was all that the line was providing , it was an acceptable way to provide an extension socket and phone .
With semi detached housing it was common for the BT 66 to be mounted at the boundary of the two dwellings served by a 5 pair underground cable , so each property used 1 pair and the cable had 3 spares ) a separate cable then taken into each house, any ‘extra’ cables to extension sockets may have been provided by a DIYer , or may have been provided as a paid for extension , but it’s been decades since anyone rented extension sockets / phones , and these extensions have long since been the householder’s responsibility, if the extension socket is not needed , remove it completely from the line ( wiring and socket ) , it may improve your broadband performance on the remaining main socket .
FWIW , if the cable from the BT 66 to the main socket were defective ( it could be 60 years old ) then it also could be disconnected and a new NTE5 could be cabled from the BT66 , but just because it’s old doesn’t mean the existing cable is faulty , if you wanted Openreach to do that , it woukd need to be proved faulty , or pay for a master socket relocation
