Is there a name attached to the Regs approval? Sometimes they're just signed by 'Building Control Team' or whatever but other times they're signed by the actual inspector. Presumably it's a different site inspector anyway? It is possible the site inspector assumed there would be a kitchen door fitted which could explain the lack of foresight. None of that excuses the not picking it up during the plan approval process of course, assuming it is as black and white as that.