A SIMPLE error on your 20p coin could mean it's worth 300 times its usual value.

A batch of 20p coins from 2008 were mistakenly minted with no dates - and two have just sold on eBay for a whopping £107.

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These undated coins, known as Undated Mules, were produced in November 2008 due to a change in The Royal Mint's manufacturing process.

Whereas coins were previously dated on the "tails" side, that year the coin-maker decided to move dates to the "heads" side.

This resulted in a mix-up where no date at all was stamped onto 20p coins that month.

The Mules were the first undated coins to be put into circulation in more than 300 years.

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Only 250,000 exist, out of 136 million 20p coins produced that month.

The eBay listing attracted five bids, before the final sale was completed on September 22.

Last month, a single one of these coins sold for more than £60 at auction, after attracting 14 bids.

The Britannia Coin Company website describes them as the "holy grail of change collecting".

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However, it is not the only 20p that could land its lucky owner a huge profit.

Last year, a 23-year-old discovered an error coin from 1982, likely worth hundreds.

And other loose change can see coin collectors get lucky too.

If your 50p has a sports-themed etching, it might be one of the ones designed for the 2012 London Olympics.

These vary in value from a handy few quid to thousands of pounds, with one error coin, featuring horizontal lines, selling for £1500 at auction this year.