Boris Johnson has been selected as the United Kingdom’s new prime minister — and is poised to lead the country out of the European Union. At the forefront of many scientists’ minds are questions about how Johnson’s leadership, including his support for a ‘no deal’ Brexit, will affect research . They fear that British science has much to lose from a messy departure from the EU .

Johnson is a controversial politician, who has served as the Conservative government’s foreign secretary and as mayor of London. He has said little directly about research during his leadership campaign. But crucially, and worryingly, for many scientists and politicians, Johnson has said that he is prepared to walk away from the EU without any future trade and immigration agreements in place.

A no-deal Brexit could happen if an agreement cannot be reached with the EU by 31 October, the date by which the United Kingdom must leave the bloc. Scientists have long said that an abrupt exit would be disastrous for UK research — instantly cutting off some funding from big-money EU science programmes, threatening collaborations and disrupting travel, hiring and collaborations.

Nature looks at what Johnson’s premiership could mean for science.

How did we get here?

Johnson takes over from Theresa May,. who after three years as prime minister failed to deliver Brexit, which the British people voted for in 2016 . She resigned in late May after her hard-won, but politically divisive, agreement with the EU on the terms of the United Kingdom’s departure failed to win support from Parliament. The agreement would have allowed Britain to negotiate its future relationship with the EU during a transition period.

May’s departure triggered a leadership contest in the governing Conservative Party. Johnson and Jeremy Hunt, a former health secretary and the current foreign secretary, were the final candidates who were put to a ballot of the party’s 160,000 members. On 23 July, Johnson beat Hunt by about 45,000 votes. He is expected to officially form a government on 24 July.

How could Johnson’s Brexit stance affect research?

Johnson campaigned for Britain to leave the EU in the run-up to the 2016 referendum (see ‘Who is Boris Johnson?’). He has been vocal about his desire to “take back control” of decisions about laws and to deliver the will of the people. He hopes to negotiate a new departure agreement with the European Commission, but says that the country will leave without a deal if nothing is in place by 31 October. In June, the EU said that the withdrawal agreement is not open for renegotiation, but that it would consider fresh talks about the future relationship between the United Kingdom and the EU if the UK position changes.

Researchers fear a no-deal Brexit because the scenario could jeopardize the United Kingdom’s ability to take part in the EU’s flagship research-funding programme, Horizon Europe , worth €100 billion (US$112 billion). UK researchers have historically been some of the bloc’s biggest winners from the scheme — garnering more than the UK government has paid in.

Immigration is another major concern because there would be no immigration treaties in place with the EU after exit day. This could cause chaos at borders and have huge ramifications for UK research — 17% of scientists in the United Kingdom are originally from other European countries.

Johnson has called for an Australian-style ‘points based’ immigration system after Brexit , which could make the country more receptive to highly skilled immigrants, such as scientists. But James Wilsdon, a science-policy researcher at the University of Sheffield, UK, says that fears about Brexit have done lasting damage to the country’s reputation as a leading destination for scientists. “We have already taken a huge knock in terms of our attractiveness since the referendum, and that will be exacerbated if we exit with no deal,” he adds.

What is Johnson’s track record with science and innovation policies?

Johnson gave scant attention to research and development during his leadership campaign. Because of that, Paul Nurse , director of the Francis Crick Institute in London — one of Britain’s premier science centres — questions how seriously he will take scientists once he is in power.

Johnson has not yet pledged to continue support for the government’s flagship research target of spending 2.4% of the UK gross domestic product on research and development by 2027, says Wilsdon.

Wilsdon predicts that other spending pledges Johnson has made — for instance, tax cuts for the wealthy and increasing police numbers — could have repercussions for science spending when coupled with the widely predicted negative economic consequences of Brexit.

“Even if we avoid a damaging economic slump of no deal, will there still be the funds to do this? It leaves us with questions about sustainability of current levels and pathway to future investment, that is my biggest worry,” he adds.

As mayor of London, in 2014, Johnson launched MedCity, an organization that connects medical-science hubs in southeastern England in a bid to create a world-leading region for research, development, commercialization and manufacturing, and to boost the economy. The scheme has attracted £14 million (US$17 million) in investment to the region so far.

What about climate change?

Johnson’s parliamentary voting record reveals that he has generally been unsupportive of policies designed to mitigate climate change. In 2016, he voted against setting a decarbonization target and against requiring energy companies to have strategies for carbon capture and storage. As mayor of London, he reduced the size of the city's ‘congestion zone’ — an area that motorists must pay to access — in a scheme intended to cut pollution levels.

What is his political style, and how could that affect science?

Johnson is not an ideological politician, so any major policy changes he makes will be about political positioning rather than strong beliefs, says Kieron Flanagan, a who works on science and technology policy at the University of Manchester, UK. This differs from the decision-making style of May, who had a history of talking about the importance of long-term science and economic policies such as her flagship Industrial Strategy, a multibillion-pound policy launched in 2016 to boost economic productivity by investing in the commercialization of research.

But Johnson’s style could also benefit science. “With Boris, you might not expect consistency and long-term visions. He is attracted to shiny projects, and there are lots of those in science,” says Flanagan.

Flanagan adds that Johnson has a reputation for not doing his homework. Bluffing in international negotiations about climate change or biodiversity, for example, could be problematic. But the civil-service machinery behind him will remain the same, so if Johnson is unprepared, he might just go with what he has been advised to do, he adds.

“Boris is more unpredictable than other politicians,” says Flanagan. For example, previously, Johnson has suggested scrapping the government Department for International Development and targets for aid spending. But in his leadership campaign, he promised to maintain aid spending.

Nurse agrees. “He changes his mind repeatedly, so it is extremely difficult to have a good idea on what he might do about anything.”

How might the cabinet change and what would this mean for science?

As Johnson assembles his cabinet — the government’s senior decision-making body — in the coming days, researchers will be hoping that he will staff key science and environment posts with people who can present a progressive face to the world, says Wilsdon. But he says there are fears that Johnson will repay those who helped elevate him to power, which could see ardent Brexiters in powerful positions.

Johnson’s brother, Jo, is a Conservative MP and former science minister. Some expect that Johnson will appoint him to a senior role in the government.