25 Pounds - Elizabeth II 5th portrait, 1/4 oz Fine Platinum

The 2017 date places this coin in the first year of the Royal Mint's Britannia platinum bullion programme, which launched alongside the established gold and silver Britannia issues as the Mint pushed into the premium bullion market then dominated by the Canadian Maple Leaf and American Eagle. Platinum Britannias of this year carry the fifth portrait of Elizabeth II by Jody Clark, introduced in 2015 — the final definitive effigy used during her reign.

Platinum's extreme refining demands meant the .9995 fineness here actually exceeds the purity standard of most sovereign platinum programmes at launch.