On Tuesday, London Councils - an umbrella group representing 33 local authorities - approved a Bill that will look to ban retailers from giving away plastic bags to stop vast quantities going to landfill.
But ACS chief executive James Lowman said there needed to be discussions over how the move would be implemented before things move forward.
He said: “We welcome the energy and commitment of London Councils. However, there are a number of unanswered questions about how the ban would work, and we remain sceptical about developing London-specific solutions.”
The decision follows a London-wide public consultation which resulted in 90 per cent of people requesting action be taken on plastic bags and 60 per cent calling for an outright ban.
A private Bill will be submitted to Parliament at the end of November by the councils.