The legal-tender exemption almost no one uses
Gold coins produced by The Royal Mint that are UK legal tender — Gold Britannias, gold Sovereigns, and the Lunar/Queen's Beast series struck as legal tender — are completely exempt from Capital Gains Tax. Not exempt up to an allowance. Exempt without limit, because HMRC treats UK currency disposals as outside the scope of CGT.
This matters more every year. The CGT annual exempt amount has been cut to just £3,000 for 2026/27, down from £12,300 three years ago. Gains above it are taxed at 18% for basic-rate payers and 24% for higher-rate payers. A gold bar or a South African Krugerrand is a chargeable asset like any other. A Sovereign is not.
Work a realistic number. You buy gold, hold it, and sell years later with a £20,000 gain. After the £3,000 allowance, £17,000 is taxable.
Same metal. Same gain. Up to £4,080 difference, decided entirely by which coin you picked at purchase. For a buy-and-hold UK investor outside a tax wrapper, there is rarely a good reason to choose anything other than CGT-exempt coins.