@Viviennemary
I'd say they are getting away with it by saying it's a ducal coronet not a crown. And they've removed the word royal.
I didn’t realise about ducal coronet, just had to google
Commonwealth usage[edit]
Depiction of a baron's coronet on a 17th-century funerary monument
In the United Kingdom, a peer wears his or her coronet on one occasion only: for a royal coronation, when it is worn along with coronation robes, equally standardised as a luxurious uniform.
In the peerages of the United Kingdom, the design of a coronet shows the rank of its owner, as in German, French and various other heraldic traditions.
Dukes were the first individuals authorised to wear coronets.
Marquesses acquired coronets in the 15th century, earls in the 16th and viscounts and barons in the 17th. Until the barons received coronets in 1661, the coronets of earls, marquesses and dukes were engraved while those of viscounts were plain. After 1661, however, viscomital coronets became engraved, while baronial coronets were plain. Coronets may not bear any precious or semi-precious stones.[1]
The coronet of a duke (a silver-gilt circlet, chased as jewelled but not actually gemmed) has eight strawberry leaves of which five are seen in two-dimensional representations.
The coronet of a marquess has four strawberry leaves and four silver balls (known as "pearls", but not actually pearls), slightly raised on points above the rim, of which three leaves and two balls are seen.
The coronet of an earl has eight strawberry leaves (four visible) and eight "pearls" raised on stalks, of which five are visible.
The coronet of a viscount has sixteen "pearls" touching one another, nine being seen in representation.
The coronet of a baron or Lord of Parliament in the Scots peerage (a plain silver-gilt circlet) has six "pearls" of which four are visible.
Since a person entitled to wear a coronet customarily displays it in his or her coat of arms above the shield and below the helmet and crest, this can provide a useful clue as to the owner of a given coat of arms.
In Canadian heraldry, descendants of the United Empire Loyalists are entitled to use a Loyalist military coronet (for descendants of members of Loyalist regiments) or Loyalist civil coronet (for others) in their arms.