You really need to sort your IT, this is not the first time you have been unable to open thing that others have no problem with.
In case you still haven't been able to access it there are 11 really good pictures.
Why would BC be required? For a Victorian house, it would have had habitable status for 100 years.Do you need building control involved in that?
You’ll probably need interlinked smoke alarms through the house, and a fire exit from the cellar.