Hi again Unky,
D side is BT's name for their Distribution side cables from their PCP green cabinets to your house(s).
Where the fibre cables from the S Yorks Project FTTCs go is entirely up to them. The telephones, if S Yorks are using the Shared (Metallic Path Facility) connection stay connected to the exchanges, but the fibre can go anywhere. If S Yorks have chosen the entirely disconnected D side lines, i.e. the Full (Metallic Path Facility) disconnection, then the phone calls will be routed via VOIP over their internet connection.
I hope that's clear !
Kind regards,
Walter