The United Kingdom and Germany have signed their first bilateral treaty since the end of the Second World War, marking the beginning of a renewed partnership focused on strengthening defence across Europe. The Kensington Treaty was signed in London by Prime Minister Keir Starmer and German Chancellor Friedrich Merz at a time when Europe is under increasing pressure due to Russia's war in Ukraine and uncertainty about the future role of the United States in NATO.

The treaty mainly promises that both countries will support each other in case of an armed attack. While both are already protected under NATO’s Article 5, this agreement adds another level of mutual support. It also strengthens cooperation in defence manufacturing and military technology.

“We see the scale of the challenges our continent faces today, and we intend to meet them head-on,” Starmer said during a joint press conference held at an Airbus plant in Stevenage.

Merz called it “a historic day for German-British relations” and added, “We want to work together more closely, particularly after the United Kingdom’s withdrawal from the European Union. It is overdue for us to conclude such a treaty with each other.”

The treaty outlines a wide defence agenda. It includes plans to jointly promote weapon systems like Typhoon fighter jets and Boxer armoured vehicles. There are also plans to develop a new long-range precision missile within the next ten years. German drone manufacturer Stark will set up a production facility in the UK to support Ukraine’s defence efforts.

The agreement clearly states that both countries will “assist one another, including by military means, in case of an armed attack on the other,” although the practical importance of this clause remains uncertain because both countries are already NATO members.

“Defence is the thread running through the treaty,” Merz said after the signing ceremony at the Victoria and Albert Museum.

Both leaders also placed this treaty in the context of broader European efforts, especially following French President Emmanuel Macron’s recent visit to the UK, during which France and Britain agreed for the first time to align their nuclear deterrence strategies.

Since Germany does not possess nuclear weapons, the treaty confirms it will maintain “a close dialogue on defence issues of mutual interest … including on nuclear issues.”

Merz said, “The E3 – Great Britain, France and Germany – are converging in their positions on foreign policy, on security policy, on migration policy, but also on economic policy issues.”

He made it clear that his visit to London just one week after Macron’s was not accidental. “It was no coincidence,” he said. “We are really on the way to a new chapter.”

As the war in Ukraine continues, the UK, Germany and France are leading efforts to maintain strong support for Kyiv. One part of their discussion included former US President Donald Trump’s suggestion that the US sell weapons to NATO allies, who would then send them to Ukraine.

Merz explained that the details of this proposal were still being worked out and that it may take “days, perhaps weeks” before the weapons reach Ukrainian forces. He also emphasised the need for clarity from the United States. “Above all, we need clarity on how weapons systems that are given up from the European side will be replaced by the US.”

Starmer also stressed the need for diplomatic efforts. “The first step is to get [Russian President] Vladimir Putin to the table for an unconditional ceasefire,” he said, according to the BBC.

The leaders also discussed forming a peacekeeping force if a ceasefire is agreed. These talks are already underway under the “coalition of the willing,” which includes the UK, France, and Germany.

Besides military matters, the treaty also deals with illegal migration. In 2024, over 37,000 people crossed the English Channel into the UK in small boats, with more than 22,000 arrivals already recorded this year.

Starmer said the treaty proves that both the UK and Germany are serious about tackling the criminal groups responsible for organising these dangerous crossings. He welcomed Germany’s plan to change its law by the end of the year to make it a crime to assist in smuggling migrants into the UK.

“We’ve discussed this at great length,” Starmer said. “[The chancellor] is now going to change the law so that we can intervene.”

Merz confirmed the change and added, “We want to drastically reduce illegal migration in Europe. We are on a good path, but we haven’t reached the target yet.”

Merz also suggested building on the UK-France migration agreements to create a three-country return deal. “The cooperation between the United Kingdom and France … has to be complemented by an agreement that we aim to achieve between the three of us: UK, Germany, France,” he said through a translator.

This proposal reflects Germany’s long-standing goal of building a strategic partnership among Europe’s major powers. Merz’s predecessor, Wolfgang Schäuble, once spoke of a “core Europe” led by Berlin and Paris. Now, Britain is rejoining that vision, even though it is no longer part of the European Union.

Although Merz expressed his regret over Brexit, he acknowledged that more cooperation is now necessary. “I personally deplore this deeply,” he said. “But we are now learning that it’s not enough, so we have to do more.”

The Kensington Treaty goes beyond defence matters. It includes efforts to increase cultural and educational exchanges, launch a joint railway task force, and allow British passport holders to use Germany’s automated e-gates.

Merz also supported more flexibility for young people. “I am glad we were able to reach an agreement so that schoolchildren and students can come to Britain more easily in the future, and the other way round can come to Germany more easily.”

Even though Starmer has ruled out returning to the European Union’s single market or customs union, this treaty shows his commitment to rebuilding ties that were damaged during the Brexit process.

As both countries prepare to raise their defence budgets to 3.5 per cent of GDP, the Kensington Treaty represents more than just a defence agreement. It reflects a clear intention for Europe to take on greater responsibility at a time when older alliances are shifting.

For both leaders, this treaty marks the beginning of a new era in international cooperation.

“We had you in the European Union and we thought that was enough,” Merz said. “But we are now learning that it’s not enough, so we have to do more.”