Some years ago I found some information on this necklace, but got distracted and never finished looking for more information!! But here is what I know.
The necklace, which belonged to the Earl of Shrewsbury, was auctioned by Sotheby's on 18 February 1960. It was purchased on behalf of SJ Phillips, the London dealers.
The lady in the centre of the image above is Maria, the wife of the 16th Earl. Below is an 1831 painting of her wearing the necklace.
Because I never investigated further I am not sure why the necklace was sold. However, at the time of a later sale the Earl insisted that the second sale was not because of financial constraints; rather that the jewels were rarely worn, and the Earl's second wife noted that, because they were so ornate, she had only worn some items once or twice.
One of the items in the second sale was the jewel seen below which was described as a pair of brooches taken from a tiara.
The Shrewsbury family obviously had other jewels at their disposal. I don't know if they were also sold.
Below is Anna Theresa, Countess of Shrewsbury at the 1902 Coronation.
Nadine, Countess of Shrewsbury also favoured pearls when she was presented at Court following her wedding.