"Just because it's biodegradable does not mean it's good. If it goes to a landfill it breaks down to methane. Only a percentage is captured," said Peter Skelton of Wrap, the UK government-funded Waste and Resources Action Programme.
"In theory, bioplastics are good. But in practice, there are lots of barriers."
Recycling companies said they would have to invest in expensive new equipment to extract bioplastic from waste for recycling.
"If we could identify them, the only option would be to landfill them," said one recycler who wanted to remain anonymous.
"They are not wanted by UK recycling companies or local authorities who refuse to handle them. Councils are saying they do not want plastics near food collection. If these biodegradable (products) get into the recycling stream they contaminate it.
"It will get worse because the government is encouraging more recycling. There will be much more bioplastic around."
Problems arise because some bioplastics are "home" compostable and recyclable.
"It's so confusing that a PLA bottle looks exactly the same as a standard PET bottle," Skelton said.
"The consumer is not a polymer expert. Not nearly enough consideration has gone into what they are meant to do with them. Everything is just put in the recycling bin."
NatureWorks has accepted that its products would not fully break down on landfill sites.
"The recycling industry in the UK has not caught up with other countries," said Snehal Desai, chief marketing officer for NatureWorks.
"We need alternatives to oil. UK industry should not resist change. We should be designing for the future and not the past. In central Europe, Taiwan and elsewhere, NatureWorks polymer is widely accepted as a compostable material."
Other users said it was too soon to judge the new technology.
"It's very early days," said Reed Paget, managing director of Belu.
"The UK packaging industry does not want competition. It's shortsighted and is blocking eco-innovation."
Belu collects its bottles and now sends them to mainland Europe.
"People think that biodegradable is good and non-biodegradable is bad. That's all they see," said Chris Goodall, environmental analyst and author of How to Live a Low-carbon Lifestyle.
"I have been trying to compost bags that are billed as 'biodegradable' and 'home compostable' but I have completely failed. They rely on the compost heap really heating up but we still find the residues."
Bioplastics compete for land with biofuels and food crops. About 200,000 tonnes of bioplastics were produced last year, requiring 250,000 to 350,000 tons of crops. The industry is forecast to need several million acres of farmland within four years.
There is also concern over the growing use by supermarkets of "oxy-degradable" plastic bags, billed as sustainable. They are made of conventional oil-based plastic, with an additive that enables the plastic to break down. The companies promoting it claim it reduces litter and causes no methane or harmful residues. They are used by Wal-Mart, Pizza Hut and KFC in the US, and Tesco and the Co-op in the UK for "degradable" plastic carrier bags.
Some environmentalists say the terminology confuses the public.
"The consumer is baffled," a Wrap briefing paper said.
"It considers these products degradable but ... they will not degrade effectively in (the closed environment of) a landfill site."
The Guardian