The UK will remain part of ITER
But to find the precise language agreed regarding ITER requires a bit more sleuthing. Specific citations about fusion research and ITER can be found in the "joint declarations" issued with the EU-UK trade agreement. Under the generically worded "Joint Declaration on Participation in Union Programmes and Access to Programme Services," the parties to the agreement formally recognize the mutual benefit of cooperation on science R&D. And scrolling down to Article 8 uncovers the long-hoped-for language: "The United Kingdom shall participate as a member of the Joint Undertaking for ITER and the development of Fusion Energy (F4E)."
Other passages reveal more about the scope of the agreement. The UK will continue to be part of EU's Horizon 2020 research program. Collaboration on fusion research at JET, the Joint European Torus tokamak at Culham, can continue with mutual funding. As part of Fusion for Energy, the UK will remain part of the Broader Approach agreement.
But for the ITER community, it is the 20 words cited above that justify a collective, heartfelt sigh of relief. UK government officials have long made clear that they hoped their country would remain in the ITER Project; but as the saying goes, the proof is in the pudding. From a legal standpoint, a bit more time will be needed for the necessary agreements to be formally approved, but in practical terms it means that we can expect the continued full involvement and participation of UK citizens and UK companies. The persistent tension that has been so troubling for UK fusion experts at ITER—and their families—has at last been resolved. The ITER team will remain intact.