Thank you Beth for searching the British newspapers for more information on this event. I did also think of the Greek Emerald tiara, but like you said; what then about the emerald necklace?
It could also be that they were mistaken for the Norwegian Emeralds, of course. Newspaper articles cannot be 100% trusted - sadly - be it modern ones or those from the past. But somehow I don't think the Norwegian Emeralds would be described as "the finest" among what must have been a gathering of such outstanding pieces.