"With a lot of these plant-based treatments, there's a lot of circumstantial evidence and not a lot of science to back it up," he told Reuters. "What we're really trying to do is inject some science into these claims."

He said scientists were hoping to show that essential oils extracted from plants such as thyme, garlic and cinnamon could have a similar effect to antibiotics, which kill harmful bacteria.

The EU ban was introduced mainly to prevent the further spread of antibiotic-resistant "superbugs," some of which can affect humans and have become a growing problem for treating hospital patients.

At the Rowett Research Center in Aberdeen, Scotland, scientist Harry Flint said that as well as plant extracts, other options were being tested, including probiotics - so-called friendly bacteria that can help fight infections.

"The consequences of not finding a solution would be that food becomes more expensive," he said.

At Britain's Soil Association, which campaigns for organic farming, policy adviser Richard Young said the ban, which still allows veterinary use of antibiotics, did not go far enough.