UK-French defence cooperation: A decade on from the Lancaster House treaties

A UK-France summit was held on 10 March 2023.

It marked the first time that the leaders of France and the UK have come together in a bilateral format in nearly 5 years. Among the issues addressed was greater UK-French defence cooperation within the context of Russia’s invasion of Ukraine, France’s new national security review and the UK’s refresh of the Integrated Review.

The Lancaster House Treaties – 2010

For the past decade, defence cooperation between the UK and France has taken place within the context of the Lancaster House treaties which were agreed in 2010.

The Lancaster House treaties are primarily about improving interoperability, the capacity to act together quickly (expeditionary capability) and the joint development of capabilities.

The Defence and Security Cooperation Treaty (PDF) provided an overarching framework for future cooperation, while a separate Letter of Intent and package of joint measures attached to the treaties provided more detail on specific programmes and initiatives that would be taken forward. The treaties envisaged the creation of a Combined Joint Expeditionary force of 10,000 personnel, the development of an integrated maritime task force by the early 2020s and collaboration in capabilities, particularly in the complex weapons sector.

The Nuclear Co-operation Treaty (PDF) was intended to facilitate collaboration in the technologies associated with stewardship of both countries’ nuclear stockpiles.

In November 2020 the Government said all the milestones set out in the Lancaster House treaties had been achieved, including the Combined Joint Expeditionary Force which achieved full operational capability in 2020.

What was agreed at the UK- France summit?

The summit was regarded as an opportunity to reset the UK-France relationship and, from a defence perspective, provide a framework for future cooperation that builds on the achievements of Lancaster House. 

The overriding ambition for the next decade is to deliver further integration of UK and French armed forces. Operational cooperation will be advanced through the Combined Joint Expeditionary Force and the coordination of aircraft carrier deployments to provide a “complementary and more persistent” European presence in regions of shared interest, including the Indo-Pacific. Armaments cooperation, particularly in the complex weapons sector, will continue with a specific emphasis on possible future synergies in air defence, long range precision strike and each country’s combat air programmes.