Pranksters are flooding eBay with listings for 'upside down' five pound notes - and some are attracting bids of thousands of pounds.
The phenomenon started with a tongue-in-cheek listing the new plastic note for a startling £65,000 and showing what was clearly a perfectly normal £5 note positioned upside down.
"New £5 bank note printed upside down. Extremely rare opportunity for the most serious collectors. Seller can confirm that this is the only known upside down £5 note in existence," it read.
But the seller gave the game away with an addition at the bottom of the listing reading: "Authenticity of note verified by Department of Upside down Printed English Denominations (DUPED)."
That listing has now been removed. However, dozens of other people have since got in on the act with their own upside-down listings, with some sellers asking a fortune: one has a 'buy now' price of £3,499.80, for example, and another of £5,000.
One appears to have received a bid of £1,000, although this may be a joke.
However, most have received no bids at all - including one offering the £5 note for £4.99 plus postage. Another, which offers free postage, has stalled at, er, £5.
With the launch of the new polymer £5, collectors have been snapping up notes with particularly low or unusual serial numbers, with some selling for hundreds of pounds.
Earlier this month, the Bank of England auctioned off a batch of low serial number banknotes for charity, with one reaching a whopping £4,150.
It plans to print 440 million of the new polymer notes, and will phase out the paper version. While they are more expensive to print, the new notes will last much longer, making them better value overall.
"The banknotes which were released into circulation on September 13th are still catching the public's attention with collectors looking to keep hold of the notes while they are still in good condition," says Yasmin Britton of collectors' site Change Checker.
"There are 999,999 new fivers with the AA01 prefix, so you never know, there's still a chance to find one with a special serial number."