They may have stopped being legal tender back in 2017, but there is still a mind-boggling number of old pound coins unaccounted for.
According to the Royal Mint, some 122 million 'round pounds' have yet to find their way back to the mint, or be deposited at a local bank.
Given they obviously aren't making any more of them, it's possible there are a few collector's items sat down the back of sofas or in forgotten piggy banks.
So which ones should you be on the lookout for?
Rarest old pound coins
According to coin collection specialists Change Checker, the 2011 Edinburgh £1 (pictured below) tops the list.
The site ranks coins on a score from one to 100: the higher the rating, the more valuable the coin is likely to be.
And the Edinbuirgh coin is the only one to score the full 100.
We've pasted the full list of Change Checker's rarest old £1 coins below so you can see if any of your old change beats face value.
In the likelihood that your coin (or coins) are nothing special, it is still worth exchanging them at your bank on your next trip (most but not all branches will accept them).
It's still money, after all!
How much are these coins worth?
Before we get to actual values, there are two key points to discuss first, starting with the fact that we aren't talking about life-changing sums here.
Those headlines you read about coins and notes selling for £1,000s only happen when it's genuinely unique; a one-of-a-kind.
They've often been out of circulation for decades or have a misprint on them that makes them so valuable to professional collectors.
The truth is that you're highly, highly unlikely to have a very valuable coin in your house, car or wherever you keep change.
Watch out for chancers
The second issue to raise is that of misinformation about values, which is hardly helped by numerous articles talking about coins being on sale with a massive price tag on sites like eBay and the like.
There's a very big difference between someone trying to sell a coin for a huge sum and another person actually paying that price. We wrote about the problem in detail in this piece: 'Rare and valuable coins are expensive for a reason'.
A lot of high-value listings are simply from people chancing their arm or are themselves misinformed, so it's up to you to do your research before selling or buying any rare coins or notes.
Most coins are worth the value that's printed on them.
Right, now that we've covered the fine print, what might you get for that 2011 Edinburgh £1 coin you've just discovered under your sofa?
At the time of publishing, the highest listed sale price on eBay is just over £30. But as we've just covered that's no indication of actual value. Instead, we've checked the confirmed sale prices and a coin fitting that description recently sold for just under £9.
So there you go. Maybe enough for a meal for two if you wait for the Eat Out to Help Out scheme to kick off next week...