10 Pounds - Elizabeth II Longest Reign, Silver Proof

On 9 September 2015, Elizabeth II surpassed Queen Victoria's 63 years and 216 days to become Britain's longest-reigning monarch. The Royal Mint issued this piece to mark the occasion — one of those rare commemoratives tied to a precise, historically verifiable date rather than a round anniversary or political convenience.

The .9999 fineness is notable. Standard British commemorative silver runs at .925; the decision to strike this at four-nines purity placed it deliberately in line with bullion-grade coinage, distancing it from the broader commemorative market.