Separation questions

Hi - my wife moved out on 10th August after long struggles for both of us to make it work.
We own 50% share of a shared ownership property, so 25% each. Rent is paid to the housing association for the other 50%

We decided to stay separated last night and get divorced a bit further down the line. Some questions i currently have are :
-Do we somehow need to make an official date for when she moved out and essentially separated? so that when we divorce we can definitively say we have been separated for a certain amount of time, and maybe i can claim a council tax reduction for sole occupant
-What are the implications of taking her name off the rent agreement for the flat? I think i also need to get her name taken off the lease as well?

I am asking this as when we spoke last night she said eventually she would want me to buy her out of the flat, but in the meantime I will be living there and paying all the rent. She has moved into a friend's house and has her own rent to pay. There is no mortgage on the 50% we own, it is paid off. No children are involved

Thanks in advance for any advice