Watch List notes:

Elizabeth II (1952-), Decimal New 50-Pence, 1973, struck on a cupro-nickel Ten Pence flan, edge plain, 11.37g, 12h (cf. Spink H2), much as struck, with hints of the rim to peripheries, an unusual error, in NGC 'Francis' holder, graded MINT ERROR ~ MS63 (Cert. #5878644-017).
The Roy Francis Collection of English Silver Rarities
Estimate: £100 - £150