My understanding from talking with my 'Service Provider' was you get a place on the 'waiting list' once you order fibre on a live phone line. No active POTS line, no place in queue.
The queue, by the way, is as long as a piece of string...
That's incorrect. Can I ask which ISP told you that?
I don't know of any ISP's who use the waiting list now.
The waiting list has also never been an automated process.
They don't automatically take x number of orders after a cabinet is full and put them on the waiting list (as you would expect a waiting list to work).
It was mainly used to put customers on the list if they had lost their port due to an error in the ordering/migration process, which was much more frequent in the early days of FTTC. There will be cases where users have persuaded their ISP to request a place on the list, but it has never been widely used.
I've only known of Plusnet and BT to use it, and Plusnet now no longer use it under any circumstances. BT likely have the same stance now unless there are exceptional circumstances (like losing your current port due to an ISP/OR screw up).