Boris Johnson pledged to abandon European environmental rules that have curtailed development of genetically modified (GM) crop plants and farm animals in the UK, in his first speech as prime minister on Wednesday.

“Let’s liberate the UK’s extraordinary bioscience sector from anti-genetic modification rules. Let’s develop the blight-resistant crops that will feed the world,” Johnson said.

Johnson also reiterated a pledge to build a rival satellite navigation system to the EU’s Galileo network and promised to change tax rules to benefit investments in capital and research.

On a busy first day in office, Brexiter Johnson also returned his Remainer brother Jo to his former brief as universities and science minister, replacing Chris Skidmore, who had served in the role since 2018.

Jo Johnson resigned from the post in January 2018, after opposing plans to cut tuition fees for universities, and subsequently resigned from government entirely in protest at a Brexit deal he said required choosing between “vassalage and chaos”.

At the time, Jo Johnson advocated a second referendum and said a no-deal Brexit “will inflict untold damage on our nation.”

He now faces strong criticism for signing up to his brother’s policy to leave on October 31, deal or no deal.

“There was a moment in time when you actually said what you thought and suddenly became a leading light of reason for this country,” Mike Galsworthy, the head of activist group Scientists for EU, tweeted on Thursday. “Now you have become a sell-out in one fell swoop.”

Fresh approach welcomed

Plant breeders were more positive about Boris Johnson’s commitment to shake up restrictive rules around GM.

Only one type of GM crop seed, Monsanto’s 810 maize, has commercial approval in Europe, in line with the EU’s traditionally cautious approach to biotechnology in food and agriculture. Any GM imports are subject to strict safety assessments imposed on a case-by-case basis.

US farming groups portray such restrictions as trade barriers and are demanding they be dropped in initial discussions with the UK over a post-Brexit trade deal.

In January, the US National Grain and Feed Association and North American Export Grain Association said a new deal could create a trans-Atlantic market "that can act as a bastion against the EU's precautionary advances and its ongoing aggressive attempts to spread its influence around the globe".

Potential gains from genetic technologies include a reduction in agrochemicals use, which would reduce the carbon footprint, said Dale Sanders, director of the John Innes Centre in Norwich, which specialises in crop genetics.

However, other researchers warned that while the UK may be leaving the EU, it should not rip up rules around GM safety assessments.

“Any technology for intervention in a system as complex as a plant or an animal must be proportionately sophisticated. Even with the latest genome modification techniques like CRISPR, it takes a great deal of work to make sure that only the desired changes have been induced,” said John Dupre, professor in philosophy of science at the University of Exeter.

As prime minister, Boris Johnson’s scope for ditching EU rules will depend on the outcome of Brexit negotiations with Brussels.

According to the withdrawal agreement drafted between the previous prime minister and the EU – the Brexit deal Johnson says is dead in its current form – EU requirements on GM would remain in UK law.

Any GM product would continue to require prior authorisation, and this would only be granted if there were no safety concerns.

And in a no-deal scenario, UK businesses would still only be able to export GM products to mainland Europe with EU marketing approval.

“You need a lawyer, not a molecular geneticist, to judge how [all of this] may be implemented,” said Huw Jones, professor of translational genomics for plant breeding at Aberystwyth University. “However, plant breeding in all its guises will clearly form part of sustainable future farming.”