Great research! Finally I have seen some good images of this rather "elusive" tiara of the Duchess. Up to now I have only been able to read about it in old newspaper articles. So thanks to Ursula and Laura and also to you Beth for posting more photos and for alerting us of this.

About the tiara worn by the Duchess in the photo from the Hampden House Ball; if it is not the diamond and pearl bandeau I would definitely say that the tiara from her husband is a very good contender here.

Also I was drawn to the lady in the background. She is wearing a rather impressive tiara. Any idea about who she is?

This new information (to me at least) also raises a question for me. I have seen a photo (alas I do not have the possibility to upload it, nor do I have a link to it) from AP Images. I saw it some time ago, but when I try to search for it now it seems to be gone. I did make a note of it though and it was dated 04.05.1937 and according to the website it was taken at the reception given by the treasurer and masters of the Bench of the Honourable Society of the Middle Temple of the Delegates of the Parliaments of the Empire. I thought at the time that the Duchess could be wearing the diamond and pearl bandeau, but after having seen the new photos today I wonder if it could also be the tiara from her husband. Sorry for not being able to publish a photo of it. Maybe somebody else has more luck in tracing the photo or more details of the event in order to determine which tiara was worn.