Yes, what is this object? This one that transformed Arnold Machin's sculpture into Pure Monarchy when the Stamp Advisory Committee asked him a diadem instead of a tiara on the royal head.
This crown was created in 1820 for the coronation of George IV by jewellers Rundell, bridge and Rundell. After him, queens has been wearing it, examples in artworks: Victoria on a portrait by Winterhalter in 1843, Alexandra by Luke Fildes in 1905 or on a picture with her daughters, Mary visiting Berlin in 1913.
The reign ofElizabeth II made it omnipresent: painting by James Gunn in 1954, on the obverse of many British and Commonwealth coins designed by Raphael Maklouf and put on circulation between 1984 ans 1997, and, of course, United Kingdom's definitive stamp series since 1967.
The circle is crowned by four crosses alterning with four ornaments each including the three symbolic flowers of the United Kingdom countries: the rose of England, the thistle of Scotland and the shamrock of Ireland.
And Wales? So long united to England that it was forgotten in this 1820 jewelry? Or had it not find its floral emblem yet (there were only the three quoted flowers on the first stamp of Malta in December 1860)? Or if the leek was there, was it judge disgraceful on a royal crown?
A wealthy ressource (pictures are tiny though, even for paintings in the public domain) on The Royal Collection website. Clic on the items in the right hand menu.