However, there are plenty of examples of genuine mistake-riddled coins fetching large amounts – eBay also carries a 1998 £2 for £225, and another from 2011 for £250, while a 2014 £2 commemorative Lord Kitchener coin is thought to be worth at least £400.These figures are themselves dwarfed by the £625 needed to buy one of the Mint’s 2017 Silver Proof Coin sets, with just 1,500 made, while the most expensive sale at auction was of a 700-year-old gold Edward III coin, one of only three known to exist, which sold for more than £5 million in 2006. Alex Cassidy, from GoCompare’s Coining It In, told The Mirror that the new £1 coin’s bi-metallic nature, with an outer gold-coloured nickel-brass band and inner silver-coloured cupro-nickel disc, left the potential for errors during the die-cutting process. Could your £1 be valuable?Credit:Jack Taylor/Getty “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,” he said.Nor should anyone be too hasty in exchanging their old pound coins before they cease to be legal tender on Oct 15.Many coin enthusiasts will be hoping to complete their collection of all 24 of the old designs, and the Edinburgh £1 dating from 2011 is already achieving £10 to £15 on eBay. As searches go, it is almost perfectly analogous to hunting for the proverbial needle in a haystack.With around 1.7 billion £1 coins currently in circulation, including the “old” pound coin, it might be thought that the chances of finding a rare example worth more than, well, £1 were infinitesimally small.Yet rare, potentially valuable new one-pound coins certainly do exist, and the evidence is on eBay. The new £1 coin has just come into circulationCredit:David Rose Of greatest interest to budding numismatists and shameless profiteers alike are the 200,000 “dummy” coins distributed to major retailers and businesses months before the official roll-out date of March 28 to enable them to recalibrate coin-handling machinery well in advance.The Mint may have described these “trial” stamped coins as of “no redeemable value”, but they are changing hands for serious sums. Bidding online appears to start somewhere between £150 and £250.Ebay is also full of what look suspiciously like perfectly normal new £1 coins being sold at inflated prices. Their owners attribute the value to their bearing the “wrong” date. As well as the trial coin for the new £1 piece, which does not appear to carry any of the filigree bevelling and holographic imaging that has led the official version to be dubbed “the most secure circulating coin in the world”, collectors have also been advised to be on the lookout for inadvertent errors that have crept into the real thing. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.