I am still intrigued about when Queen Elizabeth II has worn the Diamond Diadem.
On a Flickr album, www.queensimages.com compiled by romanbenedikhanson, I saw the following - https://www.flickr.com/photos/21116944@N08/11148376475/in/set-72157629204621257
The caption says the Queen was driven in a car to open parliament on 9 June 1955.
There is also this photo which has a caption saying HM is on her way to open parliament on 6 October 1955 https://www.flickr.com/photos/21116944@N08/13920784999/in/set-72157629204621257
Getty has only a photo of Prince Philip. That looks as if he too was in a car and the photo has the date for June 1955.
As it seems so odd for HM to go in a car, I wonder if others have any information which would verify this.
If HM was not going to open parliament, I wonder where she was going.
PS Copying links from Flickr does not seem to work. Unfortunately the photos are not numbered.
The second photo is on page 19 at the beginning of the second last row.
The first photo is on page 11 in the thirteenth row, or some might find it more easily counting from the bottom of the page. It is on the fifth last row.