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.
This commemorative crown-sized coin is a re-issue of the 2016 design for the last round one-pound coin, and is part of a series called Coins for a Kingdom.
The reverse was designed by Gregory Kenneth Cameron, the Anglican bishop of the Diocese of St Asaph in Wales; it represents the United Kingdom and features the mythical "heraldic beasts" symbolic of each of its parts: the lion of England, the dragon of Wales, the unicorn of Scotland and the stag of Northern Ireland, with the Imperial Crown at centre. | 
Search for United Kingdom: Five Pounds 2023 The Four Nations on eBay 