Media playback is unsupported on your device Media caption The BBC's Jeremy Cooke has had rare access to some genetically modified Enviropigs in Canada

In a small complex of nondescript barns set in the flat, snow-covered fields of Ontario is a scientific project which, some argue, represents the new frontier of a technology that could benefit millions of people around the world.

For others what is happening here is weird, dangerous science.

The pigs they are breeding could be among the first genetically modified farm animal to be approved for human consumption.

"I am very worried and I think people around the world should be worried about what's happening in North America Lucy Sharratt, Anti-GM campaigner

The huge controversy over the introduction of genetically modified crops is well documented, but this seems to take that debate a step further, and into even more troubled waters.

The project here is called Enviropig. The animals inside the clean, warm barns look like normal pigs and behave like normal pigs, but they are living, breathing wonders of modern science.

Each one contains genes from mice and E.coli bacteria, which have been inserted into their DNA with absolute precision.

Those genes make a small but important difference to the way these pigs process their food.

Ordinarily, pigs cannot easily digest chemicals called phosphates. That means that the stuff that comes out of the back end can be toxic and damaging to the environment. The phosphates are easily washed into waterways, where they can produce a hugely fertile environment for plants. But the plants grow so rapidly that they choke the stream or river and cause huge damage to the ecosystem.

THE ENVIROPIG Between 50% and 75% of the phosphorus present in cereal grains including corn, soybeans, barley and wheat is present in an indigestible compound called phytate that passes through the pig's digestive tract. The Enviropig is a genetically enhanced line of Yorkshire pigs with the capability of digesting plant phosphorus more efficiently than conventional Yorkshire pigs. Source: University of Guelph

The genetic modification enables these pigs to digest phosphates, which means they are less polluting and cheaper to feed.

Controversial

Professor Rich Moccia of the University of Guelph is proud of what has been achieved.

"It's the forefront of discovery in the scientific community. It's one of only two animals right now using this kind of technology. It really is mind-boggling when you think of it."

But it is controversial. To those who have campaigned so long and hard against the introduction of Genetically Modified (GM) crops, the notion of genetically engineered animals, such as Enviropig and fast-growing GM salmon, is a new front in a long war.

In Toronto, the Big Carrot supermarket is among the few GM-free outposts in North America. They have been fighting for years to hold back the tidal wave of genetically modified produce.

For anti-GM campaigner Lucy Sharratt, the very notion of transgenic animals is a nightmare.

Media playback is unsupported on your device Media caption Lucy Sharratt, of the Canadian Biotechnology Action Network, discusses her concerns

"This is an absolutely critical time when North America is at the very centre of the global conflict over genetically engineered animals - to break open a whole new area of application of this technology, which we had never imagined would be possible.

"I am very worried and I think people around the world should be worried about what's happening in North America," she says.

Clearly the debate remains deeply polarised. But there are also some indications that the debate may be slowly shifting.

Dr Mart Gross, of the University of Toronto, used to oppose the idea of GM crops and animals. Now he has changed his mind. Feeding the human population, he says, must come first, and GM animals and plants may help.

"We need to double food production," he says. "We currently have a global population of almost seven billion and we are looking at nine, 10 or 11 billion by 2050.

"Where is that food going to come from? We have to produce more from less."

The inventors of Enviropig know that it is by no means certain that government regulators will ever approve GM animals for human consumption.

But the massive challenge of feeding a rocketing global population, and doing it in a sustainable way, could shift the debate and ultimately dictate whether Enviropigs end up on our dinner plates.