One company alone, the frozen-food chain Iceland, reported a tenfold increase in sales of “bags for life” this year, the report found — 34 million bags, up from 3.5 million last year.

In promoting the sturdier bags in 2015, the government said, “Typically, you pay for these once and can return them for a free replacement when they wear out.”

Yet four years later, the campaigners’ report, titled “Checking Out on Plastic II,” found that the “bags for life” sold by the largest supermarkets this year amounted to nearly 50,000 tons of plastic, in addition to over 3,330 tons of plastic from their single-use bags this year.

Over all, total plastic packaging in Britain’s main supermarkets amounted to 995,000 tons last year, the report found, although some supermarkets were experimenting with selling more loose produce rather than relying largely on fruit and vegetables wrapped in plastic.

After its introduction, the plastic bag levy was credited with a more than 80 percent reduction in the number of bags given out by the largest retailers. The extent to which increased “bag for life” sales have countered this effect was unclear.