50 Pence - Elizabeth II 5th portrait, Decimalisation Anniversary, Silver Proof

Decimalisation came into force on 15 February 1971 — Decimal Day — ending a monetary system that had functioned, in various forms, since the Norman period. The transition required a public education campaign of unusual scale, including a BBC programme and millions of printed leaflets, because the shift from 240 pence to the pound to 100 was genuinely disorienting for a population that had used £sd their entire lives.

The 50p denomination itself was introduced two years earlier, in 1969, as a direct replacement for the ten-shilling note — giving it a quiet seniority over the decimal system it helped inaugurate.