Prime Minister David Cameron has raised the prospect of introducing laws to force store groups to slash the number of plastic bags they distribute.

Unless retailers address the issue voluntarily, legislation is on the cards he warned.

Cameron lauded the efforts of some retailers to reduce plastic bag use, which have resulted in far fewer single-use bags being issued in recent years, the Evening Standard reported.

But he warned it was “unacceptable” that the number rose in 2010.

He said: “I am very concerned about the use of single use carrier bags and the effect that they have on the environment.

“The number of bags being used had fallen considerably, partly thanks to public pressure, and due to the efforts of many major retailers.

“Companies like Marks & Spencer have considerably reduced the use of bags by charging and then donating the money raised to charity - £4m has already gone to good causes since they started charging in 2008 and they are doing more to clean up beaches over the next few years.

“But progress overall went backwards last year. That’s unacceptable and we need to do better. I want to see the numbers going in the right direction again.

“I know that retailers want to do better too but if they don’t I will be asking them to explain why not.

“They also need to know that the Government has options at its disposal - including legislating as other countries have done. We will continue to look carefully at all options in order to make sure that we further reduce the use of single use plastic bags.”

From the start of next month, retailers in Wales will have to charge 5p on plastic bags.