A mysterious 50p coin which is rarer than the much publicised Kew Gardens one has seen its value soar in recent months as numismatists cotton on to how few were minted.

In 2009, former BBC television show Blue Peter ran a competition to design an Olympic coin some three years ahead of the event held in London.

The winner, Florence Jackson then aged nine, had her design struck. It could then be snapped up for £1.99 via the Royal Mint website.

Rare 50p: The 2009 Olympics high jumper coin is starting to gain notoriety among numismatics

It was estimated that 100,000 of the commemorative coins would be shifted – but according to one This is Money reader, just 19,751 were sold.

The Royal Mint has since confirmed this is correct. It told This is Money that before a coin is launched, a maximum coin mintage figure is set - in this case, 100,000.

That coin will be minted on a rolling program according to demand and the maximum coin mintage figure may not be reached if the demand is not there.

In comparison, the Kew Gardens 50p coin, which can sell for up to £50 on online marketplaces such as eBay, had a mintage of 210,000.

One poster on the forum at predecimal.com said: 'This coin received a perfect storm to make it a collector's item.

'Zero publicity from the press, little interest from the public and the TV programme that was the reason for its birth taking a massive dive in popularity.'

They go on to add that in June, the coin was selling for £20.

Kew Gardens: This 50p can turn up in your change - and sells on eBay for up to £50

Then in July for £30, August £35 and now it is going for £45 as collectors look to add it to their collection.

The coin may have gone unnoticed as it was actually re-minted in 2011 and 2012, along with a full set of 29 Olympic coins, which many Britons have collected. In this mintage, 2.2million were produced.

It means there are 19,751 of these coins – illustrating a high jumper – with a 2009 date, compared to 2.2million with a 2011 date.

The reader who contacted us says the coin is special as it is the first to be designed by a child for the Royal Mint.

She also adds that the coin seems to have disappeared from official Royal Mint figures. As a result, it is only now starting to become recognised in coin collecting circles.

It is unlikely the 2009 Olympics 50p will turn up in your change, unless buyers have opened it from its packaging in an emergency.

Mint error: The coin on the left can fetch up to a £1,000, as collectors love an error

Another, even rarer Olympics 50p is in circulation – however, this is a coin with a minting error and thus, it is unknown how many exist.

GOT A COIN STORY? Get in touch: lee.boyce@thisismoney.co.uk

Ahead of the Olympics, the aquatics coin – depicting a swimmer underwater – was redesigned by the Royal Mint to make the swimmer's face visible.

But, before the change was made, a small batch of the coins were made with the original design. Last year, one of these coins sold for nearly £1,000.