What is the significance of the new treaty between Britain and Poland?
The Big Ask | No.20.2026
On 27th May, the United Kingdom (UK) and Poland signed the bilateral ‘Northolt Treaty’ on a ‘Security and Defence Partnership’. Recognising the increasingly volatile state of geopolitics – particularly in Eastern Europe, where the systemic threat of Russia looms large – the treaty reaffirmed the centrality of the North Atlantic Treaty Organisation (NATO) to both countries’ security and collective defence in the Euro-Atlantic, and the importance of advancing European security and prosperity.
This is the third such treaty Britain has signed with its major European allies in the past year, following the Northwood Declaration with France and the Kensington Treaty with Germany, both signed in July 2025. Being an important step taken in the development of the UK-Poland relationship, for this week’s Big Ask, we asked five experts, including Google’s Large Language Model Gemini: What is the significance of the new treaty between Britain and Poland?
Senior Lecturer, SGH Warsaw School of Economics
Senior Research Fellow, EU Programme, The Polish Institute of Foreign Affairs (PISM)
The significance of the Northolt Treaty lies less in specific military provisions than in broader political and strategic spheres. Signed in the context of Russia’s ongoing war against Ukraine and a rapidly shifting European security environment, it signals the consolidation of a bilateral partnership that is becoming central to Europe’s defence architecture.
Building on the 2017 Treaty on Defence and Security Cooperation, and UK-Poland 2030 Strategic Partnership Joint Declaration, the new treaty’s importance lies in further deepening of convergence of threat perceptions and strategic cultures. Both states explicitly identify Russia as the principal long-term threat and reaffirm NATO as the foundation of collective defence. However, the treaty also reflects an understanding that NATO frameworks alone may be too slow or insufficiently agile, hence the growing role of bilateral mechanisms for faster coordination and response.
Crucially, the agreement highlights Poland’s rising strategic weight. As NATO’s key eastern flank state and a rapidly expanding land power, Poland is an increasingly indispensable provider of regional deterrence. The treaty acknowledges this shift by embedding cooperation across multiple domains – military, industrial, cyber, and resilience – where Poland’s rapidly growing armed forces and cyber capabilities, as well as frontline position are essential.
For the UK, the partnership serves as a vehicle for re-engagement in European security after Brexit; for Poland, it anchors its role as a central node in a North and North-Eastern European security network. In this sense, the treaty is as much about shaping the future geography of European defence as it is about managing current threats.
Research Fellow (National Security), Council on Geostrategy
The Northolt Treaty brings together European NATO’s two most significant military powers. Poland is fast becoming, and in fact probably already is, Europe’s premier land power. Within a few years the Polish Army will field 24 combat brigades, more than Britain, France, and Germany combined. While there will be teething problems from such an extensive expansion over so short a time, it is a remarkable and commendable feat.
The UK, despite being in a capability trough, is in the process of modernising its forces and remains a nuclear power with impressive capabilities across a wide spectrum, especially in the air and maritime domains. As two of Europe’s most significant military powers, and with a track record of political and military leadership that takes the Russia threat seriously, the partnership could well come to define a future ‘Europeanised’ NATO. The Northolt Treaty helps provide the framework and signposts for what the next few years of deepening UK-Poland cooperation will look like.
With that said, it must also be recognised that the treaty is another in a string of bilateral treaties signed between the UK and European allies that have been signed more for their symbolism than their content. As important as symbolism is on the international stage, it is evident that answering the question of where and how the UK should cooperate more deeply with countries such as Poland, France, and Germany is still yet to be fully fleshed out.
Gemini
Council on Geostrategy Staff have prompted Gemini, Google’s Large Language Model, to reflect on this week’s Big Ask.
Signed by Sir Keir Starmer, Prime Minister, and Donald Tusk, Prime Minister of Poland, the Northolt Treaty represents a landmark deepening of defence and security ties between the UK and Poland. Hailed as the most significant bilateral agreement between the two nations in a generation, the pact carries profound geopolitical and strategic weight. At its core, the treaty addresses escalating security concerns in Europe, driven primarily by the threat of Russian aggression and hybrid warfare. It establishes extensive industrial cooperation, focusing on the joint development and manufacture of weapons, most notably a next-generation medium-range air defence missile.
By integrating defence supply chains and prioritising interoperability, the two nations aim to enhance the resilience of their defence industries and fortify NATO’s eastern flank through large-scale joint exercises in electronic, counter-drone, and land warfare. The treaty also serves as a strategic hedge against transatlantic uncertainty, offering a unified European response amidst shifting United States (US) foreign policy dynamics.
For the UK, the pact aligns with a broader post-Brexit diplomatic strategy to reset relations with European allies and stay embedded in the continent’s rearmament efforts. For Poland – NATO’s highest defence spender relative to Gross Domestic Product (GDP) – the treaty supports its ambition to expand domestic arms manufacturing through technology transfer. Beyond conventional military defence, the treaty incorporates a Joint Action Plan on irregular migration, economic resilience, and cyber defence coordination to counteract hostile state espionage and sabotage.
Co-President (Research), Council on Geostrategy
The Northolt Treaty is significant for four key reasons:
Both countries have committed, through Article 5 of the Northolt Treaty, to defend one another, and to provide military assistance, in the event of an armed attack on either nation. This is particularly important for Poland, because the UK, as a nuclear power, has agreed to provide an additional defence guarantee beyond NATO.
As with previous bilateral treaties, including those with France and Germany, as well as Norway, Estonia, and Ukraine, Britain can use its nuclear, intelligence, and defence-industrial heft to bypass the European Union (EU) as a security actor. As the UK entangles itself deeper into the geopolitics of Europe, it makes itself strategically indispensable.
Poland has proven that it now dances with the big powers of Europe. In the past, the UK has favoured the so-called ‘E3’ cosy with France and Germany. Yet Polish power and influence have grown over the past ten years, especially as the Polish military buildup has got under way, to the extent that Britain now sees it as an equal of the other two.
The two allies have used potent discourse in the treaty to exert narrative control. They identify Russia as ‘the most important long-term threat’ to Euro-Atlantic security, which will throw down the gauntlet to those governments that may be contemplating a softening of sanctions and the reopening of dialogue.
In short, the Northolt Treaty confirms the growing strength of British-Polish relations, as well as how the two countries, with similar geopolitical interests, can work together and use their growing weight to shape European security.
Professor of International Politics, University of Birmingham
Non-resident Senior Fellow at the NATO Defence College in Rome
The treaty reflects a spirited effort by the UK to engage with European states in an area (defence) where it has a lasting reputation. That reputation has been dented in recent years by the erosion of British military capability, but the UK is still one of NATO Europe’s foremost military powers. As well as Poland, Britain has bilateral defence agreements with France, Germany, Ukraine, and Romania. Specific arrangements (defence ‘roadmaps’, joint declarations, partnerships, and so on) exist with several other European states.
The UK is not unique in pursuing such cooperation. Defence bilateralism across Europe has been an accelerating trend during the 2020s, spurred by concerns over Russian belligerence and America’s increasingly conditional support of NATO. France and Germany have signed as many bilateral deals as Britain. The very same day the UK-Poland treaty was signed, Norway reached agreement with France on a comprehensive defence partnership. And unlike the UK, France is actively leveraging its nuclear capability. Nine states (Britain included) are pursuing bilateral dialogue with Paris as part of France’s ‘forward nuclear deterrence’ initiative.
Bilateralism of this sort adds to the complexity of Europe’s defence provision. Three tiers are now evident – the multilateral (involving NATO and increasingly the EU), the regional (with initiatives such as the British-led Joint Expeditionary Force), and the bilateral. These trends add up to a Europeanisation of defence – even within NATO, where the United States is stepping back. This is complexity without coordination and reflects a certain political and commercial jockeying for position among not just Europe’s traditional big three (France, Germany, and the UK), but also its rising military powers – Poland, Sweden, and Ukraine.
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