Do I have to jump the gun and port our phone number to a VoIP provider and then connect either a VoIP adaptor into my router, or will BT be providing an adaptor, with our existing number for the same purpose?
There will be no POTS and i can't see BT selling/running a VOIP service over another providers broadband.
If by BT you mean OpenReach then no they won't be providing any special adapters.
OpenReach don't want to handle the voice part which is why they scrapped ONT's with ATA (telephone) ports.
I can't see anything changing with the current plans.
VOIP and broadband via a single hub will be what the majority who want a landline will take.
It will be up to you the customer to either buy a bundled broadband and VOIP service, or a separate broadband and separate VOIP service.
should OR pull the plug on Voice over Copper before I am connected (if ever) to FTTP, what will BT do with our allocated phone number?
It will make little difference whether FTTP has reached you yet or not.
On both FTTP and FTTC it will be up to you to buy a bundled broadband/VOIP service, or separate services.
That's going to be the case for the majority.
For the few FTTP users with a 4 port ONT, they could order a dedicated VOIP service on a dedicated port on the ONT.
OpenReach sell? or will sell a very low bandwidth FTTP service intended for VOIP only.
Some people on FTTP with a single port ONT will be able to order a 2nd ONT, but CBT port and splitter capacity means this won't be an option for most.
In short, for you...
when the time comes you can take your landline number to your current ISP via VOIP, use a 3rd party VOIP provider or migrate to a bundled service from another provider.
Your current voice provider BT will definitely be selling Voice only services (VOIP) but they may only choose to do this via the low bandwidth OpenReach product described above.
That would require a 2nd pair, 2nd ONT or 4 port ONT, if you are keeping the AAISP line.
IMO none of the current big POTS landline providers will offer VOIP over someone else's broadband and well leave that to dedicated VOIP providers.