Bad news for fans of the £2 coin. Morrisons has banned the use of the bimetal beast in self-service tills at a number of stores. Someone has been substituting it for similarly sized and shaped coins of foreign ilk – reportedly the Iranian 250 rial (worth about 1p), and the Thai ten baht (18p).

“A handful of our stores have experienced foreign currency being passed off as £2 coins at self checkouts,” says a Morrisons spokesman. “While we fix the issue, some of those stores have temporarily stopped them accepting any £2 coins. Customers are still free to use them at all manned checkouts. We apologise for any inconvenience it is causing but don’t expect the fix to take long.”

It’s fairly unusual for coin-checking software and hardware to be befuddled in this way. “It’s not a particularly common problem,” says Jonathan Hilder, of the Automatic Vending Association (AVA). “This is just a substitution, not forgery; bimetal coins are very difficult to forge. What we have here is an opportunist.”

£2 coin money cash

Morrisons banned the use of the £2 coin at a handful of stores

Indeed, the problem is localised to a handful of stores in the Midlands, and no other retailer has reported trouble with the coin. Asda, Tesco and Sainsbury’s say they have no issue with the £2 coin, and a Co-op spokesman denies a report it is also weighing up a ban.

So it seems one rabble-rousing, recently-returned-from-holiday local has been taking advantage of the £2’s nickel-brassed and cupro-nickeled good nature. For the record, there are 417 million £2 coins in circulation – roughly one-third the number of £1 coins – with a face value of £831m. The coin was first issued in 1998 and weighs 12g.

The £2 coin was the first bimetal coin in the UK – a path soon to be followed by the nickel-brass £1. George Osborne used this year’s Budget to announce the introduction of a 12-sided £1 coin in 2017 – a launch that will have a much bigger impact on the retail industry than a few Iranian coins stuffed in a Morrisons checkout.

“It’s very important to The Treasury and the Royal Mint that there’s confidence in the £1 coin, and the number of forgeries was rising,” explains Hilder. Forged £1 coins now account for 3.1% of those in circulation – a figure deemed a little too high for comfort.

Such a change won’t come cheap: when the 5p and 10p coins were reformulated to nickel-plated steel in 2011-12, the cost to industry and the public sector was put at £80m. The new £1 coin is a much bigger change – though we won’t know the likely cost until the composition of the coin has been decided later this year: “This is going to involve at least a software change as well as a hardware change,” says Hilder.

Retailers had better start saving their copper-plated pennies.