Almost a third of the 500m still in circulation are locked inside children’s money boxes.

Parents have been urged to smash them open and get their youngsters spending before shops stop accepting the round pound coins as legal tender.

But one third of families have no idea that the coins won’t be taken by most shops after Sunday.

And another 1.1m households have no intention of changing over their old coins, a survey by 3D printing company 3Doodler found.

The firm’s Daniel Cowen said: “With so much to think about and do, it is understandable many parents and kids have missed news about the pound coin switch-over.

“This research suggests there will be a fair few of them wishing that they had smashed into their piggy bank a while ago to use up their old round pounds.”

Earlier this week the Treasury and Royal Mint called on people to spend or bank any remaining coins.

Adam Lawrence from The Royal Mint said: “The round pound has been in circulation for more than 30 years.

“But, as the deadline approaches, we are keen to encourage everyone to track down their fi nal coins and use them.

“After October 15, the 12-sided £1 coin will be the only £1 coin being spent in the UK.”