The Prime Minister said that supermarkets will be given a year to end their reliance on single-use bags or face a legal requirement to introduce a charge and reveal how much it raises.
Last November, Brown set a challenge for UK supermarkets and retail stores to reduce the wasteful use of plastic bags.
Brown has written a full-page article in the Daily Mail today supporting its campaign and praising retailers including Marks & Spencer, which yesterday said that it was introducing a 5p charge for plastic bags.
He said: "I praise those shops which have shown a moral lead already -- I am thinking of Ikea, which has reduced its bag use by about 95% recently, and Marks & Spencer, which just yesterday announced that it will charge for bags."
Last night, Tesco and Sainsbury's responded to public pressure by confirming that they are drawing up plans to reduce the amount of plastic bags they give away.
Some 13bn plastic bags are given away free to UK shoppers every year, and they take an estimated 1,000 years to decay.
Brown told the Mail that "the time to act is now" with the ultimate aim of eliminating the single-use plastic bag altogether.
He said: "I want to make clear that if government compulsion is needed to make the change, we will take the necessary steps.
"We do not take such steps lightly -- but the damage that single-use plastic bags inflict on the environment is such that strong action must be taken."
The Prime Minister also pointed to action taken by other governments, including the Irish government, which, in 2002, introduced a bag tax that led to a 90% reduction in the use of plastic bags.
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