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 2020 Year of the Rat coins are part of the Royal Mint's Shēngxiào Collection - a coin series dedicated to the Chinese Lunar calendar.
As the mint says:
"For centuries The Royal Mint has drawn upon its unrivalled heritage, experience, and craftsmanship to evolve and meet the needs of an ever-changing market. In 2014 we struck the United Kingdom’s first Chinese Lunar coins, introducing a new series and a United Kingdom first. The Shēngxiào Collection, named to honour the Chinese zodiac, is a celebration of the UK’s diverse multi-cultural society. At Chinese New Year, gifts and tokens are exchanged, particularly the gift of money in red envelopes, symbolising good wishes for the recipient’s health, wealth and prosperity. These Lunar coins from The Royal Mint embrace this globally observed tradition, lending a unique British angle to an ancient tradition."
"People who are born under the sign of the Rat are thought to be quick-witted, practical, adaptable, kind and intelligent. With strong intuition skills, they always easily adapt to a new environment. With rich imaginations and sharp observation, Rats can take advantage of various opportunities well. Rats are very curious, so they tend to try their hand at anything.
People born under the sign of the Rat have quick minds and dexterous hands, enabling them to make it easier to learn new skills. With an active, almost hectic nature, Rats enjoy a flexible social circle and tend to flit between friendship groups when they please. They are interested in attending different kinds of social occasions and events. They like to make new friends but they rarely have many that are very close. Rats have a charming appearance, which can attract even more friends."
This £5 commemorative coin is the first copper-nickel coin in the Shēngxiào Collection. | 
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