After being initially irritated at my chosen installation date having been rescheduled to some other random date, a new appointment was made for this morning.
The engineer called shortly before 12:00, plugged a 'whatsit' in the master socket, went to the street cabinet, came back after 5 minutes, plugged in & fired up the BT modem. As the LEDs on both the modem & router seemed to show that all was going to plan, he left and I was up & running by ~12:15 :-)

Let's hope the phone 'switch-over' is as painless !