Do you rent or own the flat ? , although you may never consider anything other than your FTTP provider, if you rent and subsequently move out , the next tenant may want to use Openreach , in which case you should ask the landlord if you can remove it as it’s not really your choice to make , TBH , the same could apply even if you are the owner as far as any subsequent occupant …but ultimately no one is checking, if you remove the socket /wiring no one will know , you just make it difficult to restore service over Openreach (not BT) should that ever be needed……if Openreach FTTP is available or becomes available, then it’s effectively redundant as it would never be reused .
As far as removing it ‘properly’ , BT are not involved, in some respects posting about it here a little pointless, and Openreach are not going to remove it for you ,when the flat was built , this socket was an integral part of it , and an easement for it to exist was part of the construction , but if it’s such an issue, and you want it removed , you need to do it yourself.
