In July the US and UK published a plan to remove all expiry dates from the the treaty which governs their nuclear sharing arrangements. The treaty, known as the Mutual Defence Agreement (MDA), was first signed in 1958 and allows for the exchange of information, nuclear materials and components of nuclear weapons and submarine reactors between the two states. The exchange of nuclear materials and weapon components under Article III bis has always been time limited under previous versions of the treaty, with extensions being negotiated by the two states every time it was due to expire.
The MDA marked the end of a period where the UK, having cooperatively developed the first nuclear weapons as a partner in the Manhattan project, was denied access to US knowledge and resources and decided to launch its own weapons programme. The sharing arrangement was controversial at the time, particularly in the US Congress. As a consequence, Article III bis was agreed after the main treaty and included a sunset clause.
The MDA provided the foundation for, and has sustained, the UK’s submarine reactor development. All nuclear warheads developed by the UK since the MDA was signed have drawn on US design work, and since the 1980s UK warhead development has very closely followed US designs. Further information on the MDA can be found in a briefing published by NIS in July 2024.
Under the proposed amendment, all references to the expiry date would be deleted from Article III bis, meaning that sharing under the article would continue indefinitely. Under text which is intended to remain unchanged, the treaty as a whole will remain in force until both states agree to terminate it. The exception to this is information sharing, which either state can end unilaterally at certain times if they give one year’s notice.
Another change puts the sharing of submarine reactors, including parts and fuel, on a reciprocal footing. Previously the treaty only allowed for the US to sell these items to the UK, rather than the other way around. This change would allow parts produced for the UK’s fourth-generation submarine reactor design, currently referred to as ‘Nuclear Propulsion Plant – X’, to also be used in US submarine reactors.
Most of the other changes in the proposed amendment are described as ‘updating terminology’ and changing obsolete language in the Government’s explanatory memorandum. These include adding more detail on information classification levels, updates to the definitions and replacing the article dealing with intellectual property. Changes to the final article of the MDA rule out using any dispute settlement mechanisms if any disagreement arises between the two states and allows them to agree supplementary ‘implementing instruments’.
Under the 2010 Constitutional Reform and Governance Act, the Government has to notify Parliament of any treaty which is planned to be ratified, and there is a window of 21 sitting days within which Parliament can pass a resolution blocking ratification until the government has justified its position. This process could theoretically be indefinitely repeated. The MDA amendments were published on 26th July, just before the summer recess, and the window for a resolution lasts until 23rd October. An Early Day Motion, tabled on 2nd September, calls for a Parliamentary debate on the amendment. There is a separate process in the US for Congress to agree the changes.
Update, 10th October 2024: The NIS Briefing on the MDA has now been updated to cover the 2024 proposed changes.