Efforts to cut down on disposable plastic bags by applying a 5p charge are being cancelled out by the sale of “bags for life”, according to campaigners.

More than one billion of the more heavy-duty bags, which contain more plastic than their single-use equivalents, are being distributed every year in major UK supermarkets.

While they are meant to cut down on the overall quantity of plastic waste, customers treating these supposedly durable item as single use means their benefits are being undermined.

The charge applied to disposable plastic bags in major supermarkets has been credited with cutting their use in supermarkets by 86 per cent.

In light of this apparent success, the government has floated plans to extend the measures to every shop in the country and increase the charge to 10p.

But while sales of 5p bags by the country’s biggest retailers dropped by around a fifth to 1.2 billion last year, 1.18 billion bags for life were sold over the same period.

The hardier bags cost between 5p and 10p, and tend to contain around twice as much plastic.

Data obtained by the Environmental Investigation Agency revealed the scale these bags are being sold in Sainsbury’s, Morrisons and other major supermarkets.

This prompted the charity to call for an increase in their cost to encourage customers to use the hardier bags multiple times.

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In an effort to cut overall plastic use, Asda, Tesco, Morrisons, Iceland and Lidl have completely stopped selling single-use bags and now only sell bags for life.

However, Iceland’s joint managing director Richard Walker told The Times the transition had actually increased the amount of plastic used.

“I’m not proud of this because beyond the headline of the fact I have just removed a quarter of a billion single-use carrier bags from circulation, these bags for life are a thicker, higher grade of plastic,” he said.

“We are selling less of them but it’s not yet less enough that it’s compensated in terms of the extra weight that they are for the fewer amount of bags that we are selling.

“So therefore I haven’t yet reduced the total amount of plastic weight, even though I have eliminated 5p carrier bags.”

Tesco also revealed to The Times it had used more plastic in the bags for life sold up until July than in the single-use ones sold in the previous financial year.

The government has pointed to its plastic bag charge as evidence of its success in fighting the “scourge of plastic waste”, with environment secretary Michael Gove saying it was evidence of Britain’s position as “a global leader in protecting our seas”.

However, campaigners called for a reappraisal of the charges applied to bags for life to see if there is any impact on the overall quantity of plastic being used.

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Sarah Baulch, the Environmental Investigation Agency’s senior ocean campaigner, said bags for life should cost £1 or more if supermarkets were to start reaping the benefits of the 5p charge.

She said too many customers were still simply using the replacements as single-use bags.

“A significant increase to the price of bags or ending sales of single-use bags completely should be a next step in reducing plastic bag usage,” she said.

“In the face of a global plastic pollution crisis, supermarkets must go beyond these minimal measures and fundamentally rethink their use of single-use plastics across their supply chains.”