Is the following feasible?
In WWII, a man owning a typical terraced house in Chelsea (say 3 floors + basement + attic) decides to build a bomb shelter underneath that basement. He finds the activity very emotionally satisfying, so he just carries on extending his basement.
The first architectural problem that arises is that the foundation walls only go down so far. What he needs to do is lower them piecemeal fashion. That is, he digs a trench (say, 1 yard wide) against the wall until he reaches the bottom. Now he adds bricks underneath.
Is there a problem here?
Towards the end of the war, the adjacent house comes on the market. Delighted, the man snaps it up, and starts digging.
Eventually he succeeds in building downwards to a depth equivalent to one and a half storeys.
He also puts in two doorways through the bearing walls between the two properties, using thick wooden lintels.
A few decades later he dies, leaving the properties (plus a sizable sum of money) to his only son. The son knew about the excavations but he had always imagined that planning permission had been obtained previously. When he has the houses surveyed, he finds out that the excavations were all illegal - and, incidentally, that the neighbours didn't know anything about them!
(He'd been away at school, then abroad in Africa, etc., etc.)
Given the son's innocence, the borough council imposes only a moderate fine, but they do order him to make the houses safe.
The son decides he would like to turn them into an hotel with a cabaret plus restaurant in the basement. He goes to a firm of architects, to ask if arches could be put into the walls, to create a large dome-shaped auditorium in the 1.5-storey space underneath the basement. (More precisely, an auditorium with straight walls but a domed ceiling.)
Expensive, of course. And maybe you don't like this plotline, anyway. But is it possible?
Thanks in advance to anyone who replies.