Watch List notes:

British Coins, George IV, pattern crown, undated (1828 or 1829), in white metal, by J. B. Merlen, large laur. head l., rev. Royal arms with lion and unicorn supporters, M in gothic script below, edge plain, 35.66mm. (ESC.265A; Bull 2353 [R6]; L&S.43), some scuffs to obverse and some porosity to reverse, very fine, extremely rare and believed only four or so examples known
Linecar & Stone refer to an example exhibited at the Numismatic Society in 1887 and also mention that two appeared in the Nobleman sale (1922)
Jean Baptiste Merlen (1769 - 1850), the French (or perhaps Flemish) 'extra assistant engraver', in practice the second engraver, at the Royal Mint.
(1000-1500 GBP)