As part of Britain’s exit from the European Union, British Prime Minister Theresa May has committed to removing the United Kingdom from the jurisdiction of the European Court of Justice (ECJ). The issue has marked a crucial redline in ongoing Brexit negotiations, dividing those who take an absolutist approach to the manner of the country’s exit from those seeking more flexibility. But the Prime Minister has been unequivocal. In her own words: “The authority of EU law in Britain will end.”

May’s stance has been poorly received across the United Kingdom’s increasingly fragmented political landscape. This is partly because the UK also intends to back out of Euratom, a European institution that provides the legal backstop to civilian nuclear activities in the UK. The reason: Euratom relies on the ECJ. A parliamentary Select Committee called the decision to leave Euratom an “unfortunate, and perhaps unforeseen, consequence” of leaving the ECJ. Former ministerial advisor James Chapman has been publicly damning of May’s position, stating that “if she doesn’t shift on Euratom … parliament will shift it for her.” Even Dominic Cummings, Brexit doyen and former ministerial advisor, has colorfully called for the UK to stick with Euratom. A cross-party group of senior Members of Parliament (MPs) voiced their concerns, threatening to derail Brexit legislation that depends on a small parliamentary majority. The government’s plans have been rapidly thrown into disarray.

So what is Euratom, why is it important, and what does it have to do with Brexit?

O Euratom! My Euratom!

The European Atomic Energy Community, known commonly as Euratom, was established by treaty in 1957. The original signatories were Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany. These states also founded by treaty the European Coal and Steel Community in 1952, and the European Economic Community in 1957. These three treaties undergird the later development of the European Union.

Euratom exists to promote and support the development of nuclear energy in Europe, by regulating the nuclear industry across Europe, safeguarding the transportation of nuclear materials, overseeing the safe disposal of nuclear waste, and carrying out nuclear research. When it was established 60 years ago, Euratom was described in its founding documents as a “nuclear common market” that enabled the free movement of nuclear workers and nuclear materials between member states. It also provides the legal framework that underpins the regulation of civilian nuclear activities; this has included the UK since 1973. The treaty establishes strict safety standards for the nuclear industry, and also governs nuclear safeguards; these ensure nuclear materials are not diverted from civilian to military activities.

Euratom is therefore historically aligned with the evolution of the EU. While established under its own treaty, it is governed by key EU institutions, including the European Court of Justice. That is why Theresa May wants to terminate the UK’s 44-year membership of Euratom.

What happens if the UK leaves?

Departure from Euratom has many consequences. Here are three.

First, it will cause disruption to the UK’s own nuclear industry. Euratom regulates, safeguards, and inspects UK nuclear facilities. The UK will need to replicate Euratom’s safeguarding arrangements under agreement with the International Atomic Energy Agency. As the UK has recently engaged in a multi-billion pound program to build new nuclear power stations, this will be a serious problem. The new building program may face significant delays if new arrangements are not in place when Brexit occurs. The clock is ticking on these new arrangements: Brexit will take place in only 19 months.

Second, nuclear research is closely linked to Euratom: This body provides almost 90 percent of the funding for the Joint European Torus (JET) nuclear fusion research facility at Culham in Oxfordshire. JET also employs 350 scientists from all over Europe. Euratom guarantees freedom of movement for nuclear experts across Europe, putting it at odds with the government’s increasingly hard line on immigration. Both funding and jobs are threatened by the UK’s departure.

Finally, Euratom regulates the import and export of radioactive and nuclear materials. This includes medical radioisotopes used to treat cancer—materials which cannot be produced in the United Kingdom. Leaving Euratom could erect barriers between patients and these essential radioisotopes imported from continental producers. This possibility has generated lurid headlines linking exit from Euratom to delay of cancer care treatments.

The government has tried to stymie concerns by insisting it will pass a new nuclear safeguards bill. If enacted, this legislation would pass on responsibilities that currently lie with Euratom to the UK nuclear regulator, the Office for Nuclear Regulation (ONR). It is by no means clear that this process will be smooth. ONR is experiencing a skills shortage due to an aging workforce. While the organization would have a far bigger task following Brexit, it may lack enough trained staff to fulfill its expanded role. This would impair ONR’s ability to regulate effectively.

Can the UK leave the EU but not Euratom?

The obvious solution to May’s difficulty would be to leave the European Union but not Euratom. Is this possible? According to Financial Times’ Brexit columnist David Allen Green: “If the government accedes to a demand from MPs that the UK not now leave Euratom, there seems no alternative but for the country formally to attempt to revoke or amend the Article 50 notification” that formally precipitated Brexit. Why? In May’s letter informing the EU of the UK’s departure, she stated that references “to the European Union should … be taken to include a reference to the European Atomic Energy Community.” The UK’s Article 50 notification included leaving Euratom. Reconsidering Euratom may therefore mean reconsidering the UK’s Article 50 notification upon which Brexit is being built.

What will happen next?

Any crossing of the redline regarding the European Court of Justice would be seen as the cardinal sin of contemporary politics: the dreaded U-turn. But support for Euratom is too widespread to be ignored. The Prime Minister may be forced to reconsider her position on Euratom. The alternative is parliamentary unrest.

If this is the case, Theresa May will probably need to reconsider the UK’s notification of Brexit. This would be extremely challenging. The general public does not want a revision of the Brexit decision. Nor does Parliament. And the EU may not allow this to happen anyway.

Disruption of the Brexit process seems likely either way. The government’s response has failed to address most key issues, being a negotiating platform rather than a statement of policy. And, as David Allen Green has said, “the Euratom issue is only the first major devilish detail” of an increasingly uncertain Brexit process. Getting this right, however hard, will build confidence that Theresa May is capable of taking the hard decisions required by Brexit. As the Euratom debacle shows, evidence of this has been sorely lacking.