@^woody^ you would think the "system" would be robust enough to prevent "bad things", but it surely doesn't. The house attached to us has been "refurbished and developed". I don't know who the inspector was, but several things have been done that should never have been passed (including a dodgy loft conversion), and the youngish couple who have bought it, must have had a survey, and still bought it...
Part L requirements (in the context of this thread), are a bit of crap legislation tacked on to what are intended to be "life safety" regulations but are increasingly being used for political objectives.
The regulations generally are intended to allow flexibility, and that is the correct approach IMO. The weak link is the interpretation by individuals, but that should be dealt with by suitable training and good management. The LABC are working hard to get comprehensive and consistent messages out through their members and partners.
The buying process is a different problem.
There is not only the issue of flexibility being applied to past building work inspections (with future parties not knowing the context of past decisions), but unauthorised changes to past work (making past approvals invalid), unauthorised work with no applications, time-limited enforcement potential, and wear and tear making past compliance potentially noncompliant.
So this is why, IMO, it's very important for buyers to get a professional opinion of that particular property at the current moment in time. And this should appraise the buyer's potential implications and liabilities of purchasing the property. And the weak links in this case are the buyer (ignorance or reluctance to spend as little as 0.001% of the [significant] purchase price on any sort of report), and the surveyor - who seem to be more and more concerned with just the visual or technical aspects of a survey, and not the building in context of property or an asset.
And the RICS are failing here. The quality of home surveys vary widely despite attempts at standardisation. The RICS seems to be more concerned with protecting their brand, and there is the constant fear of individuals or firms needing to protect their own insurance - so reluctance to say anything non-standard or meaningful.
But if surveyors were doing their jobs, they would be able to advise buyers if say the standard of work, authorised or not, or the lack of approval for a particular alteration is in fact an issue that will materially affect them.
There are wider issues with the whole sale process, but that's for another thread.