The Treasury has urged businesses to be vigilant when it comes to handling £1 coins because millions of the wrong ones have been returned in the run-up to discontinuation of old round pounds on 15 October.

The government department said cash management company Vaultex had reported currently half of the coins that had been returned to help get the old coins out of circulation in time were in fact the new 12-sided ones rather than the old round denomination.

It said the confusion slowed the transition process down by impeding new pound coins from entering circulation and keeping the old round pounds in tills and purses.

Andrew Jones, MP, exchequer secretary to the Treasury, said: “Businesses must remain vigilant when returning coins and ensure old and new coins are organised in separate packaging to make the sorting process quicker and easier.

“We also want cashiers and shopkeepers working at till points, who are truly on the front line of the changeover, to play their part to ensure only new pound coins are given to shoppers in their change.”

The government announced in spring last year that the old £1 coin would be removed from circulation to protect against sophisticated counterfeiters.