This Sherlock Holmes rare 50p could be in your pocket - how much is it worth?

A new 50p coin celebrating Sherlock Holmes has entered general circulation, meaning the great detective could pop up in your change at any point from now on.

If you do find the coin, which bears the deerstalker-and-pipe enthusiast's silhouette, it could be worth more than face value.

But since the Royal Mint is yet to confirm how scarce the coin actually is, its true value would be a mystery for even Sherlock Holmes himself.

Read on to find out which rare 50ps are the most valuable, and how likely you are to be handed one at the till.

How much is the Sherlock Holmes 50p worth?

Earlier in May, multiple versions the Sherlock Holmes coin became available for purchase on the Royal Mint website to celebrate the 160th anniversary of author Sir Arthur Conan Doyle's birth.

The design features the deerstalker-clad detective surrounded by the titles of some of his most famous stories.

The cheapest version was a brilliant uncirculated coin in a presentation pack, which is still available for £10.

Other versions, including limited edition silver and gold proof coins, retailed at up to £795 each before they sold out.

These collector's coins have since appeared on eBay, though they don't always fetch a lot.

The out-of-stock silver proof version of the coin appears to have sold for around £85 - more than its £55 price from the Royal Mint. But it has also sold for close to £40, which is significantly less.

The brilliant uncirculated version sold for a maximum of £11.50 between 23 and 28 May - just £1.50 more than its retail value. This was an exception, as it most often sold for less.

The circulated version of the coin, however, does have the potential to fetch big figures. But only if there aren't too many of them.

Is the Sherlock Holmes 50p rare enough?

The most valuable circulated 50p at the moment is the 2009 Kew Gardens coin, which goes for upwards of £100 on eBay.

It's worth so much because of its low mintage - only 210,000 entered circulation. In contrast, the 2016 Peter Rabbit coin was minted over 9 million times.

Mintage figures for the Sherlock Holmes 50p are unlikely to be available any time soon. But if it turns out to be similarly scarce, collectors could see Kew Gardens-level prices.

According to coin collection site Change Checker, the Kew Gardens 50p was overlooked for years until official mintage figures were revealed in 2014.

At the moment there is no way of knowing whether something similar will happen with the Sherlock Holmes coin.

If you do find it in your change, though, it might not be worth selling yet. Change Checker tells us that collectors would be unlikely to pay more for a circulation-quality Sherlock Holmes 50p than they would for the £10 brilliant uncirculated version, which is still available to purchase.

Which other rare 50ps should I look out for?

The Royal Mint has already released at least four new commemorative 50ps coins and coin sets this year - one of them even commemorated other commemorative 50ps.

In March, the Mint released a Stephen Hawking 50p to celebrate the influential scientist, and a full-colour Peter Rabbit 50p - following the 2016 line of non-colour Beatrix Potter character coins.

More children's literature was recognised when Julia Donaldson's Gruffalo earned its own 50p in February.

The difference between these 50ps and the Sherlock Holmes 50p, however, is that none of them have entered circulation so far.

This means the only way you'll find them in your change is if a collector accidentally spends one. For the most part, you'll have to buy them online to add them to your collection.

There are, however, a number of rare 50ps which are in circulation that you could very well end up finding. Especially if you apply a Sherlockian level of focus.

After the Kew Gardens coin, the second-rarest 50p by mintage is 2017's Sir Isaac Newton coin. The circulated version appears to have sold for a range of prices between £1.04 and £3.99 on eBay in the week leading up to this article.

There are also a number of 2012 London Olympic Games coins that regularly sell above face value online. Some sports are more valuable than others, with the tongue-in-cheek football coin that 'explains' the offside rule often selling for the most.

It's best to take eBay listings with a pinch of salt, however. Sellers can inflate prices by setting high starting bids, and could in theory manipulate the market by bidding on their own products.

Ultimately, a rare coin is only worth as much as a collector will pay for it. If you put your rare 50p on the market, you may not end up making money.

The Which? Money Podcast spoke to several coin collectors and the Royal Mint for an episode on rare coin collecting. You can listen to it here: