REMEMBER when we were all scanning our plastic fivers for a rare serial number? Well, now it's time to check your new £1 coins out...

The coin joins the UK market on March 28, with a billion already struck and ready for use.

It will feature a security-proof hologram, which flickers between a '£' symbol to the number '1', under different lights.

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But you'll have to dig a little deeper to catch the clues that make them worth more than a quid.

Money expert Alex Cassidy told The Mirror: "As with the current £2 coins, the 2017 £1 coin is bi-metallic - in this case an outer 'gold' coloured nickel-brass band with an inner 'silver' coloured cupro-nickel disc," Alex explained.

"Because of this, any potential die errors during production, which occurs when the dies have become misaligned, could be worth a lot of money.

"Punters should pay attention to both the floral crown on the reverse side for any rotations, as well as the Queen's head, which should sit directly above the new bevelled edge."

A handful of the new £1 coins wrongly dated '2016' are in circulation.

"These are possibly the rarest and most valuable ones to watch - it's possible some may slip through the net and into circulation over the next few months."

"These new £1 trial coins are fascinating, especially considering the financial precedent of the £2 trial coins in 1994, which have since become one of the most sought after collectable coins in Britain," explained Alex.

"If these new trial coins turn out to be as valuable as 1994’s, then anyone who gets their hands on them now could be sitting on a future goldmine."