@Alien8 I did a short stint during lockdown working for a BT call centre.
I never learned how to do number porting lol, but I remember clearly that there are numbers allocated to providers according to exchange locations.
If you move in an area within a different exchange box (which is not a box, but a building) your number cannot be ported.
About VOP, I know that you must get a new number.
I know this because when I switched to Sky for ISP, they automatically assign you a socket for a phone, even if you have no phone!
Sky said if I wanted to plug in a phone the number is already allocated.
I forget now how to find out your new number, because I only use my mobile, but I guess it would be in your contract.