Undated 20 pence coins should be taken to the London Mint Office or other reputable coin dealers to determine their worth. In 2009, the London Mint Office, which is unrelated to the Royal Mint, offered recipients of the undated coin 50 GBP for the 20 pence coins.Know More
The undated 20 pence coins were created in 2009 as an error of the Royal Mint. The coins were stamped with an old design of the Queen's head and without a date, and then with a new design on the reverse that was also undated. An estimated 50,000 to 200,000 of the undated 20 pence coins were released to the public.