A cross-party committee of MPs has dismissed government plans to introduce a 5p charge on plastic carrier bags in England as a "complete mess".
The Environmental Audit Committee (EAC) said current proposals are "unnecessarily complicated" and the levy is based on "wishful thinking than hard evidence".
MPs said the plan, which excludes biodegradable bags, paper bags and small retailers, is overly complicated and risks confusing consumers, undermining the potential benefits of the scheme.
Chairwoman Joan Walley said: "Ministers have managed to make a complete mess of their planned carrier bags charge by making it unnecessarily complicated."
"Carrier bags litter our streets and harm wildlife, and the government is right to want to reduce their use, " she added. "But Defra seems to have made decisions about the design of this scheme that were based more on wishful thinking than hard evidence."
The report called on the Government to drop the exemptions and apply the levy on all types of bags and retailers, including small businesses, following the example set by Wales, which has "successfully" introduced a 5p charge on all types of carrier bags, according to the report.
The Department for Environment, Food and Rural Affairs defended the plan insisting it "should not come at the cost of burdening small businesses who can choose whether or not to charge their customers".
A Defra spokesperson added: "Paper bags make only a small proportion of carrier bags and break down naturally; biodegradable bags will only be exempt if they are genuinely biodegradable."
Some eight billion disposable carrier bags are used in England every year- the equivalent of over 130 bags per person each year. In Wales, that number has decreased to 22 a year following the introduction of a 5 charge.
Friends of the Earth said charging for disposable bags is a "step in the right direction" but warned that the Government must do more to encourage recycling and slash waste in England.
Campaigner Michael Warhurst said: "Ministers must take urgent steps to slash waste and turn it into valuable resources, and save some of the phenomenal £650 million a year we squander burying nd burning reusable and recyclable materials."
Last year, Deputy Prime Minister Nick Clegg said the levy on single-use bags would come into effect after the 2015 general elections and the money raised by the scheme would go to charity.
Research shows a large majority (81 per cent) in England is willing to pay 5p for carrier bags if the money is indeed used for charity. Government experts say the levy could raise around £70 million.