I have received my copy of the Queen's Diamonds, and these brooches are featured on pages 254-'55
"The Greville Ivy-Leaf Clips
Cartier, London, before 1930 and 1937 Diamonds, platinum
These clips ... were made by Cartier for Mrs. Greville, one apparently before 1930, when a diamond was reset, and the second in 1937, using her own stones. At this point, the earlier piece was modified to match the new clip. They were bequeathed to Queen Elizabeth in 1942, and they were given to Princess Elizabeth by her parents to mark her 21st birthday, during the tour of South Africa in 1947. The Queen continues to wear the clips regularly."
[Hugh Roberts, The Queen's Diamonds, (London: Royal Collection Publications, 2012), pp. 254 - 255].