Green Central: click here to read Times Online's environment blog

Scientists and environmentalists have attacked a global campaign to ban plastic bags which they say is based on flawed science and exaggerated claims.

The widely stated accusation that the bags kill 100,000 animals and a million seabirds every year are false, experts have told The Times. They pose only a minimal threat to most marine species, including seals, whales, dolphins and seabirds.

Gordon Brown announced last month that he would force supermarkets to charge for the bags, saying that they were “one of the most visible symbols of environmental waste”. Retailers and some pressure groups, including the Campaign to Protect Rural England, threw their support behind him.

But scientists, politicians and marine experts attacked the Government for joining a “bandwagon” based on poor science.

Lord Taverne, the chairman of Sense about Science, said: “The Government is irresponsible to jump on a bandwagon that has no base in scientific evidence. This is one of many examples where you get bad science leading to bad decisions which are counter-productive. Attacking plastic bags makes people feel good but it doesn’t achieve anything.”

Campaigners say that plastic bags pollute coastlines and waterways, killing or injuring birds and livestock on land and, in the oceans, destroying vast numbers of seabirds, seals, turtles and whales. However, The Times has established that there is no scientific evidence to show that the bags pose any direct threat to marine mammals.

They “don’t figure” in the majority of cases where animals die from marine debris, said David Laist, the author of a seminal 1997 study on the subject. Most deaths were caused when creatures became caught up in waste produce. “Plastic bags don’t figure in entanglement,” he said. “The main culprits are fishing gear, ropes, lines and strapping bands. Most mammals are too big to get caught up in a plastic bag.”

He added: “The impact of bags on whales, dolphins, porpoises and seals ranges from nil for most species to very minor for perhaps a few species.For birds, plastic bags are not a problem either.”

The central claim of campaigners is that the bags kill more than 100,000 marine mammals and one million seabirds every year. However, this figure is based on a misinterpretation of a 1987 Canadian study in Newfoundland, which found that, between 1981 and 1984, more than 100,000 marine mammals, including birds, were killed by discarded nets. The Canadian study did not mention plastic bags.

Fifteen years later in 2002, when the Australian Government commissioned a report into the effects of plastic bags, its authors misquoted the Newfoundland study, mistakenly attributing the deaths to “plastic bags”.

The figure was latched on to by conservationists as proof that the bags were killers. For four years the “typo” remained uncorrected. It was only in 2006 that the authors altered the report, replacing “plastic bags” with “plastic debris”. But they admitted: “The actual numbers of animals killed annually by plastic bag litter is nearly impossible to determine.”

In a postscript to the correction they admitted that the original Canadian study had referred to fishing tackle, not plastic debris, as the threat to the marine environment.

Regardless, the erroneous claim has become the keystone of a widening campaign to demonise plastic bags.

David Santillo, a marine biologist at Greenpeace, told The Times that bad science was undermining the Government’s case for banning the bags. “It’s very unlikely that many animals are killed by plastic bags,” he said. “The evidence shows just the opposite. We are not going to solve the problem of waste by focusing on plastic bags.

“It doesn’t do the Government’s case any favours if you’ve got statements being made that aren’t supported by the scientific literature that’s out there. With larger mammals it’s fishing gear that’s the big problem. On a global basis plastic bags aren’t an issue. It would be great if statements like these weren’t made.”

Geoffrey Cox, a Tory member of the Commons Environment Select Committee, said: “I don't like plastic bags and I certainly support restricting their use, but plainly it’s extremely important that before we take any steps we should rely on accurate information. It is bizarre that any campaign should be endorsed on the basis of a mistranslation. Gordon Brown should get his facts right.”

A 1968 study of albatross carcasses found that 90 per cent contained some form of plastic but only two birds had ingested part of a plastic bag.

Professor Geoff Boxshall, a marine biologist at the Natural History Museum, said: “I’ve never seen a bird killed by a plastic bag. Other forms of plastic in the ocean are much more damaging. Only a very small proportion is caused by bags.”

Plastic particles known as nurdles, dumped in the sea by industrial companies, form a much greater threat as they can be easily consumed by birds and animals. Many British groups are now questioning whether a ban on bags would cost consumers more than the environmental benefits.

Charlie Mayfield, chairman of retailer John Lewis, said that tackling packaging waste and reducing carbon emissions were far more important goals. “We don’t see reducing the use of plastic bags as our biggest priority,” he said. “Of all the waste that goes to landfill, 20 per cent is household waste and 0.3 per cent is plastic bags.” John Lewis added that a scheme in Ireland had reduced plastic bag usage, but sales of bin liners had increased 400 per cent.

Times recommends

• Energy-saving ideas from switched-on professor
• Rooks are as clever with tools as chimpanzees
• Burping of the lambs blows roast off menu