The 20p piece is a rare “mule” coin dating from 2008.

The coin was minted without a date due to an error and quickly became a sought-after collector’s items. Prior to November of that year, the date on 20p coins would be found on the tail side. However, the Royal Mint switched it so that the date would now be next to the Queen’s head.

A rare 20p “mule” coin dating from 2008 has sold for £66 on eBay after attracting 29 bids.

The coin was minted without a date due to an error and quickly became a sought-after collector’s items.

Prior to November of that year, the date on 20p coins would be found on the tail side.

However, the Royal Mint switched it so that the date would now be next to the Queen’s head.

A mistake in 2008 led to the old format being used on the Queen’s side and the new format being used on tails side.

As a result, the first batch of British coins with no date on them was released into circulation for the first time in more than 300 years.

Around 250,000 20p coins minted in November 2008 are believed to have entered circulation with no date.

The coin was spotted by a seller in Kent, who listed it on the auction site with a starting price of £10.

The seller described the coin as being “in nice circulated condition” and said it was minted during a time when the date on the 20p piece was moved from the tails to the heads side.

They added: “Due to an error at the Royal Mint, the old format was used on the Queen’s side and the new format on tails side.

“As a result the first batch of British coins with no date on them were released into circulation for the first time in over 300 years.”

The coin sold for £66 after attracting bids from across the country.

What makes a coin valuable?

The 50 pence piece has become the most valued and collected coin in the UK, with many collectable designs appearing on its heptagonal canvas.

Its 27.5mm diameter makes it the largest of any British coin, and allows space for decorative pictures.

It has often been used to celebrate big events over the past 50 years of British history.

The rarest coins tend to be of the greatest value, with the mintage (number of coins with each design made) being the fundamental attraction for collectors.

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Along with the design, other aspects of the coin which increase value are the condition of the coin and whether it has an error in its design.

The way in which it is sold can also determine the coin’s value - while some coin collectors will bid vast amounts of money on ebay or at auction, others opt for more robust valuations by selling via a coin dealer.

Rarest 50p coins in circulation the UK?

The Royal Mint has revealed the most valuable 50p coins in its collection.

One of the rarest is the Kew’s Garden 50p, which was designed to mark the 250th anniversary of the gardens in 2009.

Only 210,000 coins were ever minted with this design.

The Kew Gardens 50p sells for £156.25 on average, but one seller received over £700 for one when they sold it on eBay.

The other rarest coins stem predominantly from the 2011 Olympics, with the wrestling, football and judo coins among the most valuable.

Only 1.1million of each of these coins were produced.

Flopsy bunny and Peter Rabbit designs which were produced in 2018 are also highly valuable.

These coins - 1.4 million of which were minted - depict the characters from Beatrix Potter’s novels and celebrate the life of the English writer and these sell for around £5.

In 2019, 500 million coins were produced, with three new 50p designs.

These included one of Arthur Conan Doyle’s Sherlock Holmes, Paddington Bear at St Paul's Cathedral and the Tower of London.

Top 10 most valuable 50p coins, according to Royal Mint

Here is a list of the top 10 most valuable coins, when they were made and how many were minted: