The Consumer Council on Tuesday painted a picture of anarchy when it comes to the online grocery world's use of plastic bags, with some shoppers getting them for free, others paying for them but not receiving them, and nobody given the chance to refuse them altogether.

The watchdog said it recently got staff to pose as ordinary shoppers and between them they made 69 orders with 11 online stores and e-commerce platforms, including those of the city's supermarket chains.

They found that the number of plastic bags sent out varied even for identical orders, while different fees were charged on different occasions for the same number of bags from the same retailer – or no charge was made at all for the bags that arrived.

And while it appears sometimes people can get away with free bags, not everyone is as lucky.

"Some online stores/e-commerce platforms charged a plastic bag fee or packaging fee without providing any bags," the council lamented.

It added that it only got the right number of bags that it paid for in six of the 69 trial orders placed.

Nora Tam, who chairs the council’s research and testing committee, called for some clarity from retailers.

“Online stores, e-commerce platforms should clarify their charging policy and calculation criteria for plastic bags or packaging, so the consumers should have all information to make the informed decision,” Tam said.

Hong Kong's shopping bag charging scheme means retailers have to charge at least HK$1 for most bags they give out.

The council said retailers should offer customers the chance to refuse plastic bags altogether – an option people have when they shop in person.