wonderboysteve,
its certainly my recollection of MW's explanation, he made the point more than once, that it was Marshall's decision to discontinue which triggered the end of flight and RR would have continued (but not with anyone else such as Cranfield). It sounds like you know him personally and may have heard things differently. If I've misunderstood I apologise - his comments were made at the Vulcan Restoration Trust Christmas event so a good 40 or 50 others in the room also listened to what he said, they may have heard differently to me, though he seemed quite clear to me.
Nutloose, I have also wondered the same thing. The Silica gel incident couldn't have built confidence, to say the least.
Anyway, whether RR or Marshalls felt enough was enough, or whether it was a joint decision hardly matters now.