China has banned supermarkets from handing out free plastic bags. Maybe they should do the same for online grocers here.

The latest online survey from The Grocer 33 shows that the combined total number of plastic bags used by the retailers was 54 - a big increase on the 41 used in our last survey - making a mockery of retailers' promises to cut plastic bag use.

Only one of the five major online retailers - Asda - used fewer plastic bags to deliver the 33 items ordered by our mystery shoppers than for the previous survey three months ago.

The other four - Ocado, Sainsbury's, Tesco and Waitrose - all increased the number of bags they used.

Sainsbury's was the worst offender. It used 18 bags for 32 items - a shocking average of 1.7 items per bag.

"We are extremely disappointed that our policy of packing groceries in as few bags as possible was not followed," said a Sainsbury's spokeswoman. "We take this very seriously and we are investigating with the store."

Sandra Bell, supermarkets campaigner for Friends of the Earth, said: "We keep hearing claims from the big supermarkets about being green grocers. But it seems that they can't even manage the simple task of cutting down on plastic bag use for online deliveries. Such a poor performance on a basic issue like this casts doubts on the likelihood of them delivering real change on more fundamental environmental problems such as cutting climate change emissions."