Leslie Field wrote in 1987 that "The Queen has another necklace that she wears only on private occasions. Made around the turn of the century by the Revivalist jewellers Carlo and Arthur Giuliano, this long openwork gold necklace is set with multicoloured sapphires and zircons and decorated with green enamel leaves."

The link below is to a pdf version of an interesting 1975 ten page article on the Giuliano Family by the esteemed Geoffrey Munn.


http://wartski.com/wp-content/uploads/2016/05/The-Giuliano-Family-The-Connoisseur-1975.pdf

See necklace displayed on page 5. Its description on page 6 says its from the Royal Collection and is an "Enamelled gold and multicoloured sapphire necklet", length = 16 inches.
There is no mention of zircons as stated in Leslie Field's description, and this is a choker necklace which doesn't match what Field wrote.
However the small green enamel leaves are very visible. I am guessing that Leslie Field's description had errors.