The campaigners said the store collection points have contributed to Sainsbury’s and Tesco claiming they are close to achieving their voluntary packaging recyclability targets.
The schemes have also led to an increase in soft plastic packaging carrying labels telling shoppers to “recycle with bags at large supermarkets” instead of “do not recycle”, the groups added.
However according to the Waste and Resources Action Programme (Wrap), the UK’s infrastructure has limited mechanical recycling capacity and is mainly used for commercial waste rather than post-consumer waste.
In a legal briefing published with the investigation, non-governmental organisation ClientEarth said soft plastic recycling claims in the form of product labels, in-store signage, and website content are misleading consumers about the environmental impact.
Sainsbury’s said it has recently improved its signage to help encourage more customers to recycle soft plastic waste in its stores. The improved signs include details on which items are accepted and the ideal condition they should be in to allow the supermarket to recycle them.
A spokesperson said: “We’re always seeking ways to positively manage the end-of-life of our packaging.
“We collect a small volume of flexible plastic overall in-store. The majority is in good condition and they’re recycled.
“However, when materials are soiled or damaged, then they may need to be converted for energy, which is managed by our supplier. Feedback is important to us and we’d welcome any suggestions on how we can improve our efforts in this area.”
Tesco said that while the investigation found materials were sent to an accredited processing site in Turkey, this was a supplier error as the supermarket’s materials should not have been sent to that location.
A spokesperson said: “We have a clear plan to remove packaging wherever possible and to reduce, reuse, and recycle it where we can’t.
“We work hard to recycle the materials we collect. For example our Bags for Life, and in some cases we are even able to use it for projects such as fruit and vegetable planters donated to schools, or park benches donated to the NHS.
“When it is not possible to recycle the collected plastic, we put it to alternative uses to avoid these materials going to landfill, for example using it for energy recovery.
“We know there is a lot more progress to be made, and the infrastructure to recycle soft plastics at scale in the UK and the EU has a long way to go.
