That does seem a bit odd but I have a vague recollection that an ONT, connected to the fibre and powered on, can be tested remotely. However it cannot enter service without the serial number being registered by an engineer adjacent to, and in eye-sight of, the ONT.
Thanks for your input.
The Openreach team were assigned to my property as I was the lead person in getting FTTP fitted where I live.
The OR engineer made a phone call to make sure the ONT was ready to roll.
He told me all I need is to join a router and I am good to go, no engineer visit needed.
The serial number of my ONT is visible on another ISPs website when you do a search on their products with your post code, one ISP said they could get me up and running in 2 days.
It now appears that BT tried to do a check on my ONT remotely when it was not plugged in and that threw out an error and a need for an engineers visit.
The salesman never told me to plug it in there and then he said plug it in the day before your super hub 2 is due to arrive.
BT have now cancelled my order and are setting up a new one, apparently.