Cardboard boxes being stored in people's garages is continuing to cause shortages of the material, the boss of a major packaging company has said.
Miles Roberts, chief executive of DS Smith, said the firm was working with local councils to improve supplies of cardboard to recycle into new boxes.
DS Smith, whose largest UK customer is Amazon, used to get bulk supplies from High Street shops and restaurants.
But lockdown and a surge in online home delivery has changed the supply chain.
Mr Roberts said: "We've found that, frankly, all those old cardboard boxes that we need, all that old newspaper that we need to recycle, has actually been stored in people's garages and in their refuse bins."
He told the BBC's Today programme: "We've really been working on a local authority by local authority basis to say 'How can we improve the return of that material?' so we can make it into new packaging, get it back out into the supply chain."
Cardboard has been in short supply for retailers across the UK since January.
Before lockdown, cardboard and other material used by shops could often been seen at the roadside and at storage facilities ready for collection by recycling firms. It meant, said Mr Roberts, that cardboard quickly returned to the supply chain.
Supermarkets have also experienced shortages of cardboard packing with Asda, Lidl and the Co-op finding they had to switch to, for example, plastic boxes for their eggs. That sparked criticism on social media about their green credentials.
Asda said there was a "shortage of the pulp used to make the cardboard boxes" that was "affecting all retailers". It added, though, that its plastic boxes were 100% recyclable.
'We've switched to plain brown stock boxes'
Wholesale popcorn business Popcorn Shed has had cardboard supply problems since January.
Director Sam Feller said the company was not able to get brand-printed corrugated boxes from "any of its UK suppliers".
Before Covid and Brexit, branded boxes would arrive three or four weeks after the initial order, but now "delivery dates bear no resemblance to when the order turns up" Mr Feller said.
Often the delays have come with a price hike because cardboard box manufacturers say they cannot get the usual material.
"We've switched to plain brown stock boxes and are larger too which means more pollution and wastage as a result," Mr Feller said.