Hi,
We would refer you to our Property Income Manual:
PIM2025
PIM3010
and Business Income Manual
BIM46915 this covers what is a repair and capital expenditure.
If the work done has restored your property to what it should’ve been then that is a repair and would usually be an allowable deduction.
If you alter or improve it then it is not a repair and the expenditure is capital.
Please see
PIM2505 for expenses incurred before rental business begins.
Thankyou.