Like many other mints, the Royal Mint issues bullion coins in precious metals, having much higher intrinsic value than their face value. Most of these by tradition are measured in troy ounces of fractions thereof, but the mint also introduced metric coins measuring one kilogram of pure metal (they are actually fractionally heavier as a whole, to account for the small amount of other metal in the alloy).
The 1 kg gold coins are denominated as One Thousand Pounds (£1,000), although their intrinsic (bullion) value is much higher than their face value. The coins vary in design depending on the occasion (they are "one-year" types usually issued in parallel with smaller denominations with the same reverse designs).
The coins are legal tender but are not intended for circulation. They are targeted at bullion investors or collectors who appreciate the special editions as pieces of art.
This coin was issued in memory of Queen Elizabeth II, the longest reigning monarch in British history.
The Royal Mint says about the series:
On 8 September 2022, Her Late Majesty Queen Elizabeth II passed away peacefully at Balmoral Castle in Scotland. For more than seven decades, Her Majesty upheld a promise she made in which she pledged her heart and devotion to the people of the United Kingdom and the Commonwealth.
Marking the historic succession from one monarch to another, the coins in the Memorial Coin Collection honouring Queen Elizabeth II are the first to feature King Charles III’s official coinage portrait designed by acclaimed sculptor Martin Jennings. | 
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