A expert has excited collectors after suggesting that certain 20 pence pieces could be worth a "small fortune". Taking to , Coin Collecting Wizard implored Brits to "stop spending 20p coins", urging them instead to scrutinise their to see if they possess a particularly sought after specimen. "One from 2008 with no date is worth £60," he disclosed. "Normally, the date on the 20p is on the reverse right under the crown, but in 2008 something strange happened."

The expert proceeded to describe how, in that year, a select batch of 20p coins were minted with a novel obverse - the now-familiar shield motif, which superseded the old Tudor rose emblem.

Yet, in this case, an error occurred and the fresh obverse was erroneously paired with the original effigy side, resulting in some undated coins being inadvertently released.

"This is what we call a mule error, when mismatched dyes are used - and this one slipped into circulation without anyone noticing," he detailed. "Normally, 20p coins have the date on the back, but if you check and there's no date on either side then you might be holding the rare one."

The Coin Collecting Wizard added: "These 20p coins are rare, but not impossible to find. In average condition they go for £60 plus. People are still finding them in their change even 15 years later - so if you pay with cash, check every 20p."

He concluded by pointing out that, while 50,000 of these coins may have entered circulation, this figure is merely a "drop in the ocean" in terms of UK coinage.

1. Mint errors: Look for coins with minting mistakes, such as doubles dies (designs appearing twice), off-centre strikes, blank planchets or overstrikes. These errors often make coins highly sought after by collectors.

2. Misprints: Coins with misspelled words, dates or other irregularities.

3. Time: Older coins, particularly those issued centuries ago, can be rare, but not all old coins are valuable. Rare historical coins, especially from limited production runs or old empires, may be worth more.

4. Historic significance: Coins tied to significant events or periods, such as certain monarchs' reigns, can also hold value.

5. Limited production: Coins with a small number of copies minted or those that were only issued for a short period are typically more valuable.

6. Rareness of year: Certain years are more valuable than others, especially if fewer coins were struck that year.