“It also doesn’t take into account the wider environmental effects, such as littering associated with light-weight carrier bags. You only have to ask yourself when was the last time you saw a cotton bag blown into a tree or ingested by a sea bird!”

Oxo-degradable additive firm Symphony Environmental also criticised the EA report for failing to consider the effects of littering.

In a statement about the EA report, the firm said that no credit had been given for the main purpose for which oxobio plastics have been developed “so that they will harmlessly degrade then biodegrade in the presence of oxygen if they escape the collection processes and find their way into the environment”.

Symphony added that there is no evidence in the report degradable plastics encourage littering. It said: “A litter-lout would not know that oxo-bio products were biodegradable unless they were so labelled, because they look and feel the same as normal plastic.

“It is absurd to imagine that such a person would examine a label before deciding to discard as litter. In any event a lot of litter is accidently discarded, without any conscious decision.”

The EA report – Life Cycle Assessment of Supermarket Carrier Bags – was requested by the previous UK Government and remained unpublished for three years.  It stressed that whatever type of bag is used, the key to reducing the overall impact is to reuse it as many times as possible, whether for shopping, bin liners or other purposes.

Jarvis advocated this view and said people should reuse “whatever bag” as many times as possible”.

He continued: “So if you have a ‘bag for life’, make sure you keep it with you when you’re shopping and reuse it. If you forget it and pick up a plastic bag, make sure you reuse it.

“The report shows that, as with most lifecycle analyses the answer is ‘it depends’. While ‘bags for life’ or cotton bags have greater environmental impacts earlier in the product lifecycle, these can be mitigated with the right consumer behaviour later on.

“And clearly these types of bags are intended to have a long lifespan and to be used many times over. The report also shows that equally, if a lightweight carrier bag is thrown away after just one use its environmental impact is not negligible and we must always remember that it’s the sheer mass of single-use bags that cause the problem, not the odd bag here and there.”