Could they match the description in the book 'Boucheron - The Secret Archives', page 162 about the Greville jewellery: 'pendant earrings composed of two large pear shaped cabochons suspended from a line of four detachable diamonds'?
From a different book (Crown Jewel - A year in the life of the Queen Mother by Ian Lloyd):
Even when I consider different angles I don't think picture no1 and no2 are a match. What do you all think? Perhaps there is a better picture available in one of your 'vaults'?