Tristan da Cunha is one of the few UK Overseas Territories not to have its own currency. In the old days no-one needed money - goods and services were exchanged by barter trade. Even when the Island was garrisoned by British Forces during World War II, the common "currency" was cigarettes or potatoes. With the establishment of the Fish Factory and an import/export trade with South Africa in the early 1950s, Rand notes and coins were used. However, when Tristan was resettled in 1963 after the exodus caused by the 1961 volcanic eruption, the returning Islanders brought back with them the money saved during their stay in the UK. Thus, pound sterling notes & coins entered circulation, and are today long established as the official currency (although visitors to the Island may also pay in Rand, US Dollars and Euro, which is converted at the prevailing rates of exchange).
Tristan does, however, have a Commemorative Coins Ordinance which enables the Governor (with the prior approval of the British Secretary of State for Foreign & Commonwealth Affairs) to "cause coins to be made and issued to commemorate notable events of importance to Tristan". Coins made and issued under the provisions of this law are, in fact, legal tender on the Island (not that they would ever be used as such because their collectible or metal value is likely to exceed their face value).
The Ordinance has been used from time to time. However, design and production costs, when combined with the logistical challenges of bringing the commemorative coins to the Island for distribution and sale, resulted in a net loss of revenue for the Tristan Government which, after the economic decline in the mid 1990's, was unable to afford to produce further issues.
A change for the better happened in November 2004 when, with the approval of the Governor and the Secretary of State, the Tristan Government entered into a five year agreement with the Commonwealth Mint & Philatelic Bureau Ltd (formerly known as London Mint Ltd). This innovative partnership enables Tristan to select and approve designs for proposed issues, with the company arranging production and distribution to collectors via established dealerships worldwide. Production costs are met by the income from sales and, in addition, the Government receives a royalty on each coin sold. This provides a welcome revenue stream in addition to traditional income from the fisheries sector, a modest amount of tourism, and sales of stamps and souvenirs. The agreement was subsequently extended until 2022.