Union Jack and the White Eagle. Significance of the Poland-UK Defence Treaty

On 27 May Donald Tusk and Keir Starmer signed a long‑prepared Polish-British Treaty on Security and Defence Partnership. For London, it is a flagship attempt to reset Britain’s security relationship with Europe after years of post‑Brexit estrangement, for Warsaw – another brick in the wall of forward deterrence.

What was signed – and why it matters

The 2026 Poland-UK defence treaty finalises a decade-long effort to establish functional bilateral cooperation. The first defence and security treaty, signed in 2017, was narrowly focused on hard military cooperation outside the EU structures. Following the full-scale Russian invasion of Ukraine in 2022, the extent of cooperation widened, producing a string of major armaments contracts and a joint declaration of strategic cooperation until 2030.

The new Northolt treaty is broader in scope and more political in tone, with the common denominator across its pillars being the shared threat perception of Russia. The preamble explicitly names it as ‘the most important long‑term threat’ to Euro‑Atlantic security and commits both governments to countering its ‘hostile actions’. Beyond classic defence issues, the treaty extends into foreign‑policy coordination, energy security, protection of critical infrastructure, cyber and wider societal resilience, including civil‑defence structures – precisely those areas left untouched in earlier bilateral documents. This aligns with Prime Minister (PM) Starmer’s earlier assertion that ‘there is no British security without Europe, and no European security without Britain’, a line he has repeatedly used to argue for deeper UK-EU defence links.