Watch List notes:

(g) NGC PF60 CAMEO | George III (1760-1820), New Coinage, Posthumous Issue, Pattern for a Five-Sovereign Piece, the so-called "Proof Five-Pounds", 1820 LX, by Benedetto Pistrucci and William Wellesley Pole for the Royal Mint, GEORGIUS III D: G: REX F: D: laureate head right, signed PISTRUCCI beneath truncation, rev, St George and Dragon, PISTRUCCI below ground line, small W.W.P. on ground by Dragon's tail, DECUS ET TUTAMEN. ANNO REGNI LX. on edge in upright raised letters, 39.91g [617.0grns], 6h (L&S 207 this coin listed; W&R 177 [R4]; Cuff 1646; Bergne 1247 = Halliburton-Young 464; Montagu [1890]; 556; Durlacher -; J S Jenks -; La Renotière 24-26; Hamilton-Smith III, 173; Clarke-Thornhill 369; Mitchell 123; Douglas-Morris 145; Selig 1158; Slaney II, 411; Hocking 1796; EGC 888 [R4]; GH 95; Spink 3783), a tiny scratch before eye and two tiny digs behind tie, with cabinet hairlines in largely matte but otherwise residually brilliant fields, the usual die softness to denticles above GEORGIUS, a most captivatingly bold extremely fine, of diminutive size but of mighty reputation as the famous Pistrucci rarity with only 25 originally struck, and this unseen at auction in 60 years, in NGC 'St Helier' holder, fairly graded PF60 CAMEO (Cert. #6769435-004).
Provenance
The St. Helier Collection of English Gold Coins,
Spink, by private treaty, 19 March 1963 - £1,925.0.0,
A H Gilbert, Glendining, 13 March 1963, lot 98* - £1,750.0.0 - extremely fine and extremely rare, only twenty-five struck [Spink]
, ,
https://www.ngccoin.uk/certlookup/6769435-004/60/
Estimate: £150000 - £200000