Written by Margaryta Khvostova. Rita is a PhD student at the Politics & International Relations department, University of Surrey, specialising in security, hybrid warfare and human rights.
The Russian invasion of Ukraine in February 2022 shattered assumptions about European security. For the first time in decades, full-scale war returned to the continent, exposing not only the limits of conventional defence but also the growing danger of hybrid threats, which include cyberattacks, infrastructure subversions, disinformation campaigns, and election interference across Europe and the UK. The status quo was no longer tenable.
What the war made brutally clear is that no country can guarantee its security alone. Alliances are indispensable, yet even the strongest can reveal cracks under pressure. NATO, the cornerstone of Euro-Atlantic defence, has been tested from within and without, while America’s gradual retrenchment underscores Europe’s need to stand more firmly on its own feet.
For Britain, the question is especially sharp. Since Brexit, defence has barely figured in the EU-UK agenda, with NATO and bilateral deals filling the gap. Yet Britain remains a leading military power, with the resources and ambition to shape Europe’s security future. The challenge is clear: outside the EU, can the UK become a fulcrum of Europe’s security architecture, or will it find itself sidelined?
Britain’s success: setting the pace for the European security response
Britain has proved itself a reliable “friend in need” since Russia’s full-scale invasion of Ukraine in February 2022. Its support has been comprehensive, and covered military, financial, and diplomatic areas, but above all, it focused on strengthening Ukraine’s long-term resilience.
This commitment predates the full-scale war. In 2015, after Russia’s annexation of Crimea, London launched Operation Orbital, a mission to train and professionalise Ukraine’s armed forces to NATO standards. Since 2022, that effort has expanded dramatically. Today, through the Operation Interflex, the UK has trained more than 50,000 Ukrainian soldiers, while also spearheading the Air Force Capability Coalition to prepare Ukrainian pilots for F-16 jets, which was a vital step in boosting Kyiv’s combat readiness.
Britain has also stood out for its willingness to act first. London pushed the boundaries of military aid, delivering NLAWs, Challenger 2 tanks, and Storm Shadow cruise missiles ahead of allies, often prompting them to follow suit. These bold moves helped set the pace for the wider coalition supporting Ukraine. More recently, the UK announced that it will collaborate with the Ukrainian industry to manufacture and co-develop advanced military equipment under a landmark technology-sharing agreement, boosting British jobs while enhancing the national security of both nations.
Diplomatic leadership has reinforced this military role. The UK was the first G7 state to act on the Joint Declaration of July 2023, signing a 10-year Security Co-operation Agreement with Ukraine in early 2024, later reinforced by the symbolic One Hundred Year Partnership Agreement in 2025. Both underscored Britain’s intent to be a long-term guarantor of Ukraine’s security.
Perhaps the clearest sign of Britain’s ambition came with its leading role in the Coalition of the Willing, a multilateral initiative co-led with France. Now numbering around 30 states, the coalition is designing a standby reassurance force that could be deployed to Ukraine in the event of a ceasefire – not to fight at the front, but to deter renewed aggression. Britain co-chairs the coalition’s planning groups, positioning itself as not just a supplier of weapons, but as a strategic convenor of European security.
Beyond Ukraine, London has worked to embed itself in Europe’s wider defence framework. The Trinity House agreements with Germany in 2024 deepened defence cooperation between the two countries. Britain has also strengthened its role in the European defence with the Joint Expeditionary Force and the Weimar+ group alongside France, Germany, Italy, and Poland. Renewed Franco-British collaboration has kept support for Ukraine flowing, while at the EU level, Britain is exploring opportunities to cooperate on the new €150 billion “Security Action for Europe” (SAFE) programme, a symbolic reset of post-Brexit relations. Finally, Britain’s defence exports have further reinforced NATO’s northern flank, with Type 26 frigates and potential Type 31 deals worth around £10 billion boosting Scandinavian navies and revitalising the UK’s own defence industry.
Taken together, these efforts show the UK not only as a decisive early backer of Ukraine, but also as a long-term architect of Europe’s security order, a role it has pursued consistently since 2022 despite political change at home.
Britain’s challenge: navigating the margins of EU defence
Despite these achievements, the UK’s influence in Europe’s security order remains constrained. Brexit left Britain outside the EU’s defence structures, limiting its ability to shape decisions from within. Unlike partners such as Norway, Switzerland, the US, Serbia, or even Ukraine, the UK still lacks an administrative arrangement with the European Defence Agency (EDA) – a gap that restricts access to EU-led projects and planning. While the newly announced UK-EU Security and Defence Partnership signals a step forward, in practice, London continues to operate from the margins of the EU’s Common Security and Defence Policy.
This sidelining has roots in the years immediately after Brexit. Under the banner of “Global Britain,” successive governments prioritised projecting influence worldwide rather than embedding the UK in Europe’s security institutions. Between 2016 and 2022, London remained detached from EU foreign and defence policy, leaving bilateral arrangements and NATO as the main channels of cooperation. Only Russia’s full-scale invasion of Ukraine forced the UK back into Europe’s strategic spotlight, not through Brussels, but through NATO, coalitions, and direct state-to-state agreements.
Yet even within this sphere, challenges persist. Britain’s heavy reliance on its special relationship with the United States creates vulnerabilities that most EU members do not face. The UK is deeply intertwined with Washington militarily, diplomatically, and especially in the intelligence field. If the White House were to downgrade its commitment to European security, London would face a sharper strategic shock than its continental partners, forcing it to recalibrate its transatlantic dependence and European engagement.
Finally, Britain’s efforts are complicated by the fragmentation of Europe’s own security landscape. Different groups, such as NATO, the EU, and regional clusters, often pull in overlapping but not always coordinated directions. While London has skilfully positioned itself in several of these arenas, the lack of a coherent pan-European framework makes it harder for the UK to translate its contributions into lasting influence.
Looking ahead: Britain and the future of European security
Britain now faces a historic opportunity to turn its wartime leadership into a lasting role in European security. London has already shown itself to be a reliable partner for Kyiv, but credibility will depend on whether it can help build enduring security guarantees alongside the EU. This means not only maintaining training and weapons deliveries but also supporting Ukraine’s domestic arms production and reconstruction. At the same time, the Coalition of the Willing can become a test case for operating independently of the United States.
For Britain, integration with Europe’s defence structures is now less a question of symbolism than of necessity. Signing an administrative arrangement with the European Defence Agency would allow the UK to fully participate in joint projects. This would strengthen Britain’s influence over practical defence initiatives and give substance to the emerging UK-EU Security and Defence Partnership.
At the strategic level, London will need to balance its two “special relationships” with Washington and Brussels. Its historical dependence on the US remains an asset, but it also carries risks if future American administrations pull back from Europe. By contrast, closer security cooperation with the EU would give Britain more strategic depth and resilience. Choosing not between the US and Europe, but finding a way to align both, may prove the only sustainable path for a post-Brexit UK seeking to remain a cornerstone of European security.
