I have been looking into the information available online regarding King Haakon VII's State Visit to the United Kingdom in 1951 in order to create a page on my blog about it.
The information regarding the first day has already been posted under the blog. Should you wish to read more about it you are very welcome to visit on: https://regalevents913271078.wordpress.com/blog-2/norway/haakon-vii/1951-norwegian-state-visit-to-the-united-kingdom/
The details available on the Queen's jewels are sadly very vague (as sadly was the norm at that time), but at least there is a photo of Princess Elizabeth making her way to the State Banquet which makes it possible to see what she wore.
So now I am looking into the second day of the visit. King Haakon hosted a banquet at the Norwegian Embassy in the evening and "luckily" photographers were on site to take pictures of the guests as they arrived. So for this occasion we have photographs of both the Queen and Princess Elizabeth - and even of Lady Salisbury in a tiara. The latter must be a clear indications that even "lesser important" guests were photographed. But so far no photos of others have emerged in my search. How happy I would have been digging into these old archives which must surely contain photographs of all (or most) of the guests.
Anyway... when looking at the complete photo of the Queen as she arrived the Embassy by car I suddenly realised that Princess Margaret must be the lady sitting next to her, though she is barely visible. Though it is possible to see that she is wearing a tiara. I just can't make out which one... could it be the Lozenge tiara?