The UK was subject to the 1957 Euratom Treaty from joining the European Community in 1973 to leaving the European Union on 31 January 2020. All nuclear material in the UK not intended for defence purposes was subject to reporting to, and inspection by, the Euratom safeguards inspectorate during this period.
The UK signed an Additional Protocol in 1998 to the “Agreement between the United Kingdom of Great Britain and Northern Ireland, the European Atomic Energy Community and the International Atomic Energy Agency for the Application of Safeguards in the United Kingdom of Great Britain and Northern Ireland in Connection with the Treaty on the Non-Proliferation of Nuclear Weapons”. The AP enhanced the IAEA’s ability to verify the peaceful uses of nuclear material within the UK by providing additional inspection powers and access to information.
Euratom is a separate body from the EU, but it is governed by the EU Commission and linked to the EU's legal framework. This necessitated the UK's withdrawal from it as part of the Brexit process. In order to maintain the extent and coverage of nuclear safeguards and to minimise the amount of adjustment required by UK nuclear operators the UK negotiated a new Additional Protocol with the IAEA that was signed on 7 June 2018 to replace the UK's existing Additional Protocol to the Voluntary Offer Safeguards Agreement with the International Atomic Energy Agency (IAEA) and Euratom. The UK then passed domestic legislation through the “Nuclear Safeguards (EU Exit) Regulations 2019” to establish the UK's domestic safeguards regime following its exit from Euratom. This enabled the UK to meet its international non-proliferation obligations, including those with the IAEA, when it came into force on 31 January 2021.