Available exclusively through the Royal Mint website to UK residents, only 250,000 have been made.
Shane Bissett, director of commemorative coins at the Royal Mint, said: "The Royal Mint has celebrated moments of national and cultural significance for over 1,000 years and, as a result, our commemorative coins are deemed very collectible."
The coin was designed by Benedetto Pistrucci and features the embossed image of St George and the Dragon.
"It is a beautiful work of art and at a price more people can afford," he added.
The £5 coin received much negativity when they were not accepted in shops or banks, rendering them worthless, except for in a collection. However, the Royal Mint has expressed that this coin is more for collective purposes than practicality.
Shane Bissett said: "We hope this new £20 coin will spark a future love of coin collecting amongst young and old alike and a greater number of people get to appreciate the craftsmanship that goes into producing all of our nation's coins."
This coin will be the first in a series of £20 coins that will be issued to commemorate significant British events.