The UK is in a unique moment in its numismatic history, as the £1 coin, our core unit of currency, changes over from a simple round shape to a 12-sided design complete with two different colours of metal and an engraved surface hologram effect.

Like the recent launch of the polymer £5 note, the 12-sided pound coin launch has got collectors on the hunt for rare and unusual examples – but unlike a bank note, a coin does not have a unique serial number. So what makes one pound coin rarer than another?

  1. First dates

Although the new £1 coin launched in March 2017, the first examples of it were actually minted in the previous year, so look out for 12-sided £1 coins marked 2016.

It’s not clear how much these will be worth in the future – some have already sold for many times their face value and the Royal Mint describes 2016 12-sided £1 coins as ‘scarce’, although in fact more than half a billion were struck.

  1. Minting mistakes

Mistakes in the minting process make individual coins genuinely unique, so look out for alignment errors between the two faces of the coin.

For example, the new £1 coin should have a point at the bottom – where two of its 12 sides meet – and this should align with both the ‘hologram’ and the lowest point of the Queen’s portrait; if any of these elements are out of alignment, you may have a rare coin on your hands.

  1. Llantrisant mintmark

The Llantrisant mintmark is a ‘cross crosslet’ – a shape similar to a crucifix – and appears above the ‘E’ in ‘ONE’ on a special edition of the 2016 12-sided £1 coin.

In theory those particular coins will go straight into collections and never enter circulation, but it’s worth looking out for the Llantrisant mintmark especially if you have a £1 coin dated 2016, as it could substantially increase its value as a collectible.

  1. Closing the circle

Finally, it might be worth hanging on to a few good examples of the last round £1 coins to be minted – they’re everywhere now, but as October 2017 approaches the round pound should gradually disappear for good.

This makes mint condition ‘old’ pound coins dated 2016 a collector’s item for the future, while good quality 1983 £1 coins – the first year the coin was issued – are also likely to rise in value over time.