Let me make it more plain for you: only the BC will/can have a judicious opinion of the quality of the work.
Oh so wrong RNR. BC only inspect work to make sure it passes the building regulations in force at the time of the build. Nothing to do with quality (if you look at the crap being turned out on building sites at the moment)
The work a BC inspects either passes or fails building regs. If something fails, it's not necessarily the quality of the work at fault, but the quality of the materials used.
Who's to say BC have any idea that this work is going on?
Just spoken to a BC officer, who told me that a lot of their involvement is the honesty of the householder / builder, or grassing by neighbours. They no longer have the staff or time to tootle around their patch, and notice work going on.
Yes, I know that uncontrolled work can be dangerous, render mortgage and insurance invalid, and can make resale very difficult, but apparently, it still goes on.
The BC told me that recently, a householder phoned up for advice, but refused to give their address. The work as described needed BC, but the householder knew that the officer would never find them, unless they gave their address themself.