Scientists have been given permission to grow genetically modified plants that could help protect against heart disease.

The Department for Environment, Food and Rural Affairs (Defra) has given the go-ahead for the field trial of a crop of GM camelina plants, the seeds of which are modified to produce fish oils. The oils could provide feed for farmed fish, meaning that fewer fish need to be caught from the sea, and ultimately could be used in health supplements or as an additive in foods such as margarine.

Scientists at Rothamsted Research Centre in Hertfordshire, who will run the trial, described the decision as a significant milestone for research into genetically modified plants.

Fish oils, or omega-3 long-chain polyunsaturated fatty acids, have been proven to be beneficial for human health and to help protect against coronary heart disease. It is also hoped the crop, if grown commercially in the future, might reduce the burden of over-fishing. About 80% of the fish oil harvested from the oceans is fed to fish grown in farms.

Researchers spent 10 years designing a sustainable way to produce the oil before successfully growing the engineered plants in lab conditions. The trial was announced in January, but has been given the go-ahead after a public consultation.

Professor Johnathan Napier, lead scientist of the project, said: "We have made considerable progress over the last 10 years in designing and developing these plants and my colleagues and I are very happy that we can now test the performance of these plants in the field, under real-life conditions."

The particular oils that benefit the health of fish and humans, called EPA and DHA, are not in fact produced by fish themselves but instead accumulated by eating marine microbes. Napier's team took up to seven genes from algae that produce the fish oils and transplanted them into oil seed plants called camelina. It naturally produces short-chain oils and has been grown as a food crop for centuries in southern and eastern Europe and is used a biofuel crop in North America.

The research is part of a project to find out how seeds could be enhanced to benefit the population's health.

The experiment will start by the middle of May this year, with the plants harvested in August or September. Some seeds from the plants will be used for analysis, while the rest will be destroyed under the conditions of the consent.

The GM inspectorate of the Food and Environment Research Agency will carry out regular inspections.

Professor Martin Parry, acting director of Rothamsted Research, said: "We are delighted to be in position to carry out the field trial and to further assess the potential of these GM plants to contribute, as one of many solutions, to the important environmental sustainability issue of providing omega-3 fish oils."

The trial will be funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

Professor Jackie Hunter, chief executive of the BBSRC, said: "This research is seeking to provide an alternative source of omega-3 oil for the aquaculture industry that is seeking new ways to maintain and increase its sustainability.

"After many years of BBSRC-supported laboratory research this project has reached the point where only a field trial will show scientists if this could work in real-world conditions. I am pleased that the team are now in a position to proceed and will be interested in hearing their results."

Emma Hockridge, head of policy for the Soil Association, which represents organic farmers, called the move a "waste of scarce public funds".

She told Farming UK: "GM crops are making farming less fair, more risky and no more sustainable. Instead, we support practical science and innovation that addresses real needs, is genuinely sustainable and puts farmers in control of their livelihoods."