Digital voice is not dependent on full fibre to the premises, but it appears to be fibre customers that are predominantly being switched.
The choice is entirely yours whether you switch from standard broadband to FTTC, but again, standard broadband which is fed from the exchange is also being phased out as the fibre supplying your cabinet doesn't necessarily have to come from your local exchange. If the copper phone line and ADSL is phased out, it would allow that exchange to be closed.
As Keith has said though, if you are switched to BT Digital Voice, the TP Link 9970 wouldn't work so you would either have to revert to a BT Smart Hub or take up a third party VOIP service for voice instead.
Normal broadband (ADSL) will continue being supplied from exchanges that have 21cn equipment (MSANS), however the exchange equipment that provides dial tone and call routing. will be switched off at some point, and the phone part will be carried over VOIP, so some form of terminal equipment, ie the Smart hub 2 is needed.
There are many areas that only have ADSL available.
For landline only services, some alternative adapter will have to be provided. Alarm service may have to be provided this way, or directly via the Internet.
See https://digitalwholesalesolutions.com/2019/10/the-bt-openreach-pstn-and-isdn-2025-switch-off/#item4
As you are moving to FTTC, at some point in the future, you will be told that your phone connection will be moving to BT Digital Voice, and you would have to use the Smart Hub 2, if you want to retain the phone service.
I rather suspect that copper MSANs will disappear and only fibre MSANs will remain.
Thanks to you both for your combined help and advice .
we've decided to go ahead with the switch to fibre and so ordered the TP Link model suggested earlier to hopefully (at least for now ) resolve my original issue on wifi switch off .
I'll have to deal with the complications of the Digital Voice switchover whenever it arises for our location .
Thanks again
Update
Ok so the new T Link W9970 router arrived and i have it set up and working ( minus the Wifi as i wanted) but i have a question re the setting up process when the switchover to Fibre .
I have notification the Fibre is due to start tomorrow but will i have to re configure the TP Link or will it recognise any difference . BT says i may lose a connection briefly but of course they are referring to the Smart hub which of course i am not using .
So basically i'm wondering if i need to change anything BEFORE the switchover to fibre , or what should i do if i lose connection and it doesn't come back on .
For example
Will i have to adjust VDSL/ ADSL2 setting - (currently the TP Link recognised ADSL) Or will i be staying ADSL due to location and only having FTTC ?
Following instructions here i set up the TP Link with Username "bthomehub@btbroadband.com" and the PW "bt"
Is this going to stay the same and be unaffected - or should i be using the PW on the back of the unused Smart Hub BT supplied ?
Hopefully i'm worrying about nothing but in case of need i thought i should check with you guys in case there's anything i need to do to adjust the TP Link to the changeover .
The W9970 will work on VDSL just fine, but you will need to run the setup wizard again, and select the VDSL BT option.
The login details are the same as for ADSL.
As @@Keith_Beddoe says, you will need to reset the TP Link and run the wizard again when you are transferred to fibre as the settings are different to ADSL.
ADSL connects using PPPoA whereas VDSL uses PPPoE.
Thanks to you both once again for your advice and explanations .
Your help is much appreciated .