UK-USA Mutual Defence Agreement

The Agreement between the UK and the USA for Cooperation in the Uses of Atomic Energy for Mutual Defence Purposes 1958, also known as the Mutual Defence Agreement (MDA), allows the United States and the UK to exchange nuclear materials, technology and information. It was the result of an amendment to post-war US non-proliferation law, which exempted allies that had made substantial progress in developing nuclear weapons from the general ban on exchanges that might lead to nuclear proliferation.

The most important part of the MDA is time limited and is due to expire at the end of 2014. An amendment to the treaty, which will extend this deadline to 2024, must be ratified by both States and brought into force by the end of this year.

The Government published its amendments to the MDA as Command Paper 8947 on 16 October 2014. Under the Constitutional Reform and Governance Act 2010 both Houses have the opportunity to oppose ratification should they so wish, but only the House of Commons has the potential to block the treaty indefinitely. If neither House passes a resolution opposing ratification within 21 sitting days, the Government can go ahead and ratify the treaty.

Critics argue that the MDA, as amended, contravenes the parties’ obligations under the Treaty on the Non-Proliferation of Nuclear Weapons 1968 (NPT).