High Street retailers support cutting back on plastic bags but have stopped short of backing an outright ban, the London Assembly has heard.
Tesco, Sainsbury's and Marks & Spencer (M&S) said they were committed to reducing the usage of carrier bags.
But they said a city-wide ban would place an unnecessary administrative burden on small retailers who have outlets in different regions.
The hearing follows London Councils' move to ban throw-away plastic bags.
The London Local Authorities (Shopping Bag) Bill is due to be deposited in Parliament on 27 November.
About 1.6bn bags are used in London every year and only one in 200 of these is recycled, said London Councils - which represents 33 boroughs.
'Demonising bags'
Major high street retailers were answering questions about their use of throw-away plastic bags by the London Assembly's Environment Committee on Thursday.
Committee chairman Darren Johnson said authorities needed to build on the public's appetite for change.
"We are pushing on an open door," he said. "It is vital that retailers and government realise this and move things on at a quicker pace.
"Germany has removed the plastic bag from its high streets. Ireland has done it. France has done it. What's stopping us?"
"Carrier bags serve a useful function "
An M&S spokeswoman said the firm had been running a carrier bag charge trial in Ireland which it planned to extend to south-west England.
"The policy is more about encouraging customers to change behaviour rather than introducing an outright ban," she said.
A Sainsbury's spokeswoman said the use of its free carrier bags had dropped by 10% in the last six months compared to last year.
"The decrease equates to a saving of 85 million free disposable bags, which prevents 750 tonnes of bags from going to landfill," she said.
Meanwhile, Tesco said in a statement that carrier bags served a useful function.
A spokesperson said: "Rather than demonising them and restricting the customers' right to choose, we will continue to find intelligent ways to reduce the number of bags we issue while not penalising customers."
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