Compliance vs quality
Compliance means meeting a minimum legal standard. Quality means well-designed, well-built, durable, and as expected. Building Control verifies the first; nobody is contractually obliged to verify the second on your behalf.
Where homeowners get caught out
Settling for 'it is signed off' as if that meant 'it is good'. A signed-off boiler still leaks if it was sloppy work. A signed-off roof can drip from day one.
The missing role
An independent advisor — historically the Clerk of Works, today services like BuildJourney — is the only party whose remit is to watch the build on your behalf, beyond minimum compliance.