The issue is when he puts a concrete floor in and not suspended. Technically he would be asked to duct that vent to an airbrick. BCO won't let you put a sub floor vent in that location if there is a chance it could be capped off. Even if he went suspended and backed his vent to it you end up with part B issues by breaching a compartment wall and would likely end up needing itumescent seals.
It's simply not worth allowing it
It's simply not worth allowing it
Two doors down part of the floor is solid and part is suspended.... weird but true!