Some people see GM food as a ground-breaking scientific idea that could help to end world hunger and reduce global pollution. Others see it purely as 'Frankenstein foods' on 21st century menus, bringing health and environmental disasters. But what are the real scientific facts behind the newspaper headlines?

Scientists can manipulate the genetic code of life to produce plants with new characteristics never seen in nature. They can isolate any one gene from any organism like an animal or bacterium, and insert it into a completely unrelated species like a plant. The possibilities are almost endless - Scientists can insert a gene from a bacterium into a grape to make it resistant to viruses. Or they can engineer maize that resists drought or potatoes that resist pests, so farmers can use less pesticides on their crops.

For thousands of years we have been tampering with the genes of plants by traditional breeding. But there's a key difference here - with traditional plant breeding genes cross within the same species. But GM allows plant breeders to break the species barrier. And for critics this is fundamentally unnatural.

The fear is that the proteins produced by these foreign genes might be dangerous. Either because the protein itself is poisonous or because it might alter the chemistry of the plant so that the plant becomes toxic. Detailed tests are performed on the plants to discover if they are substantially biologically and chemically the same as before modification and if they have become toxic or allergenic.

Critics believe that no amount of testing can ensure that GM crops are completely safe. They believe that there is too much we don't understand about the complex genetic makeup of living organisms. And that even though there is little evidence so far, there may be a risk that genetic modification could cause effects so unexpected that they will be missed by all the tests biotech scientists carry out.

In contrast genetic engineers claim their work is safer and more predictable because they are moving just one or two specific genes, and they can more easily test the effects.

But those who campaign against GM have another fear: that the genes from the engineered plant will spread throughout the plant world, creating new strains of superweed and superbug we cannot control.

Horizon explores the key elements of scientific facts to try to answer the ultimate question: do the dangers of GM foods outweigh their benefits?