A documentary about intensive pig farming due to be screened at the Guardian Hay festival on Sunday is facing a legal threat from one of the companies it investigates. Pig Business criticises the practices of the world's largest pork processor, Smithfield Foods, claiming it is responsible for environmental pollution and health problems among residents near its factories.
The film was due to be broadcast on Channel 4 in February but was cancelled because of legal fears. A planned screening at the Frontline Club in London earlier this year was also called off.
On Wednesday London's Barbican centre was forced to delay a screening of the film after Smithfield's lawyers wrote a letter saying that the film was defamatory and included untrue claims. The show went ahead when the filmmaker, Tracy Worcester, signed an indemnity taking personal responsibility for its content.
A spokesman for Smithfield said that the company had never threatened to sue the filmmaker or tried to prevent the film being screened, but had requested that inaccuracies or false allegations be removed.
He would not say whether the Hay screening would be stopped, as Smithfield had not yet viewed the re-edited film.
Smithfield controls more than a quarter of the processed pork market in the US, and is expanding in the UK and Europe. It slaughtered 26m pigs in 2006, with sales of $11.4bn (£7.6bn) and profits of $421m.
Pig Business shows the cramped conditions in which pigs are reared, similar to those of battery hens, and claims that waste is inadequately disposed off, leaking into the surrounding environment.
Worcester interviewed people who live near Smithfield farms in the US, where the company started out, who complain of health problems including asthma and digestive illnesses, and fishermen who report that stocks have been destroyed.
The film documents the company's move to Poland, where locals claim to experience similar health problems.
Worcester, who spent four years making the film, said: "It's crucial that consumers are able to watch this so they know what is being done to their food."
Smithfield's poor environmental record was documented in Felicity Lawrence's book Eat Your Heart Out, where she notes that the company was fined $12.6m for illegally discharging pollutants into the Pagan river in Virginia.
Smithfield admits that mistakes were made in its US farms, but says that it has since improved its environmental record. The company refutes claims that pigs are mistreated.