At the time of decimalisation in 1971, the United Kingdom Crown coin (equal to 5 shillings) was redenominated as a 25p coin and pieces struck prior to 1990 - all the way back to 1818 - continue to be legal tender for that amount. The old denomination had been a regular circulating coin in the 19th century, but in the 20th century it became more of a commemorative denomination.
The Royal Mint continued issuing commemorative coins in the same format - using the traditional coin dimensions, but in copper-nickel. These were initially also denominated as 25 pence but the "Crown" was changed in 1990 to a commemorative £5 (five pound) coin, having the same dimensions and weight but with a face value twenty times as great.
The denomination is used to mark special occasions, usually royal in theme, rather than for use in general circulation. Although not circulating, these coins are legal tender.
The 2024 Year of the Dragon coins are part of the Royal Mint's Shēngxiào Collection - a coin series dedicated to the Chinese Lunar calendar.
The mint says:
"The Lunar Collection continues with a coin celebrating the Year of the Dragon. Those born under this sign are said to share many of the dragon’s desirable characteristics such as confidence, courage and adventurousness."
This £5 commemorative coin is the fifth copper-nickel coin in the Shēngxiào Collection. It was released on 4 September 2023, in advance of the Chinese Lunar Year of the Dragon (10 February 2024 - 28 January 2025). | 
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