This tiara was worn by Princess Margaret, Countess of Snowdon on several occasions (including her wedding) 

Poltimore Tiara

Designed as a graduated line of cushion-shaped and old-cut diamond clusters alternating with diamond-set scroll motifs, each surmounted by old-cut diamond terminals, to the collet-set diamond line, mounted in silver and gold, circa 1870, 19.2 cm. maximum diameter, convertible to a necklace and eleven brooches, with screwdriver and brooch fittings, in fitted blue leather case

Made in 1870 by Garrard for Lady Poltimore, the wife of the second Baron Poltimore and Treasurer to Queen Victoria’s household 1872-1874. Sold by public auction on 29th January 1959 for £5,500 as ‘a highly important tiara’ belonging to the Right Honourable Lord Poltimore, who was the fourth Baron Poltimore (1882-1965).

The Delhi Durbar Tiara