Consumer group says retailers' use of mixed materials recycling is confusing customers and leading to more landfill.
Coffee shops are failing to make it easy for customers to recycle the estimated 2.5bn takeaway cups thrown away each year in the UK, a consumer group warned on Tuesday.
The investigation by Which? found that consumers were confused by retailers' use of "mixed materials", which make recycling a headache, and urged providers to take more environmental responsibility.
More than half of the 2,471 people surveyed who buy takeaway drinks admitted that they dispose of their paper cups in the general waste bin, the research revealed.
While disposable cups are made predominantly of cardboard (about 95% by weight), they also contain about 5% polyethylene in the form of a thin coating inside the cup. David Powlson, an expert in paper recycling and principal at Poyry Management Consulting, said: "This is great for keeping your coffee warm and the cup from going soggy, but not so great when you come to realise that most UK paper mills are unable to process paper mixed with other materials."
Which? said that attempts by retailers to stem the tide of unrecycled cups varied enormously, and called on them to do more. It complained: "While all showed they try to address the recyclability of paper cups, we thought none of them go far enough."
Of the five major brands selling takeaway hot drinks in the UK, Starbucks said it is aiming to increase the number of drinks it serves in reusable cups, and also offers 25p off for customers bringing their own mug.
The bakery chain Greggs insists that disposal of cups once they have been taken out of its stores is the consumer's responsibility. Costa Coffee has slightly reduced the weight of the 140m cups it uses each year, and both Greggs and Costa point to their recycling logos as evidence of environmental responsibility.
But the investigation concludes: "Just putting a logo on the cup does not mean to say you will be able to recycle it once outside the shop … More clarity is needed for consumers on what mixed-material items can be recycled in which recycling bins or facilities. And ideally it should be made possible to recycle paper cups alongside cartons."
Which? has published a new interactive tool for consumers who are not sure about how to recycle a particular product.