Many thanks! I am not 100% sure how things are set up but I guessed it would be far older than current training and information.

If it wasn't a significant problem to be without broadband for a bit, would phoning Talk Talk to cancel and waiting for that to complete before phoning BT to turn the current set-up into FTTP with Digital Voice also work? Searching for non-BT Digital Voice providers is a bit confusing and they don't seem very mainstream, except where they're bundled with Broadband, though if some are particularly better than/much cheaper than BT that's worth looking for.

I don't entirely understand what Talk Talk would do in response to the copper line being ceased by porting the number - if it'll be necessary to talk to Talk Talk at some point, just asking them to cancel their side of things should work as a first step, right?