Require void left from the removal of external window bricked up. No need too make good as block work will be concealed at later stage.
Window void is first floor and was historically an external wall which is now part of a separating wall between original house and added self contained flat.
External side of window void is accessible from self contained flat bathroom which is currently stripped out revealing work area.
To assess previous stud wall joists in said flat bathroom which lay below a now decommissioned gravity water tank on roof. If deemed non – load bearing and/or structurally required to be removed.