LONDON — Keir Starmer will welcome German Chancellor Friedrich Merz to London Thursday to sign the biggest U.K.-German treaty since 1945 — and this time, they do want to mention the war.

Despite sitting on different sides of the political spectrum, the two men have more in common than initially meets the eye. Crucially, center-left Prime Minister Starmer and conservative Merz have a shared ambition to provide leadership on Europe’s defense.

The two leaders will use the visit to finalize a wide-ranging pact that goes big on security cooperation. It will include promises to develop a new long-range missile system and a mutual assistance pledge, spelling out that a threat to one country would likely be seen as a threat to the other, as first reported by POLITICO. Merz’s trip has gained fresh impetus after U.S. President Donald Trump’s announcement this week that he is ready to turbo-charge the supply of weapons to Ukraine.

London and Berlin are expected to confirm collaboration on quantum technology, artificial intelligence and other longer-term projects too, including offshore energy links in the North Sea and a rail connection between Germany and the U.K.

Yet warm words will likely gloss over some of the more fundamental challenges both leaders face.

Starmer will be eager to shout about measures to crack down on illegal migration — but it’s unclear how far any steps announced Thursday will take either side towards easing the huge domestic pressure they face on the issue.

Brothers in arms 

A lawyer in his 60s who ascended to Germany’s top job with relatively little political experience, Merz has a fair few things in common with his British counterpart. 

The pair have both faced sharp demands to cut immigration since they entered office, from which they’ve sought some respite on the global stage. Both have produced unexpected gambits to massively boost defense spending as the U.S. pivots away from Europe. 

While Starmer has endeavored to match the previous U.K. government’s strong backing for Ukraine, Merz is seen as more hawkish than his predecessor Olaf Scholz, bringing the UK and Germany into closer alignment. 

A German government official, granted anonymity to speak candidly like others in this piece, described the relationship between them as “excellent.”

They added that Merz was impressed by Starmer’s ability to “express himself very precisely,” particularly when dealing with Trump.

Starmer’s administration has courted Berlin assiduously, pledging to strike a defense agreement with Germany before taking office last year and seeking to rebuild relations with the EU.

Nick Hopkinson, a former director of Wilton Park, the Foreign Office’s agency for fostering German-British relations, said: “The key thing for Germany is that now that U.K.-EU relations have been reset, that opens up avenues for closer cooperation.”

The two men have met multiple times in recent weeks, at international summits and on a train to Kyiv with France’s Emmanuel Macron in May. A Chancellory insider said Merz was particularly keen for Starmer to be involved in that trip.

Triple threat

The German leader’s visit to London cements the third side of a European “triangle alliance” after Macron’s State Visit last week, as the three powers try to shore up support for Vlodomyr Zelenskyy. 

A British minister said the three-way coalition was of increasing importance, and that Germany’s forced step back during the transition period between Scholz and Merz had “definitely been felt” in London.

On that trip to Kyiv with Macron, Starmer and Merz sat at opposite ends of the train. As Starmer walked through the train, he declared: “If you want to get to Germany, you have to get past France.”

The comment appeared to be a reference to France’s somewhat more guarded stance on U.K. participation in EU matters since Brexit.

Nicolai von Ondarza of the German Institute for International and Security Affairs (SWP) think tank said: “Merz has put special emphasis on integrating the U.K. into European security initiatives, and there is a real ambition to coordinate on defense.”

Building on the Trinity House Agreement signed last year, the leaders are set to announce joint export campaigns for jointly produced equipment, while working together on a new missile system with a range of over 2,000 km to be delivered in the next decade.

Merz’s arrival in London also provides a chance to discuss Trump’s new drive to send American weapons to Ukraine. A British diplomat said they were extremely pleased with the outcome following intensive discussions with France, Germany and NATO that predated last month’s summit at The Hague.

They said “anything that gets more U.S. weaponry into Ukraine faster is good news,” confirming the U.K.’s support for the plan, in common with Germany, but in contrast to France, which was not on an early list of backers.

Merz and Starmer will be able to pore over the nitty-gritty, such as who pays for what and in which framework, along with more specific details like whether Europeans will buy U.S. weapons to be delivered to the battlefield, or whether they will give Ukraine weapons from existing stockpiles and buy replacements from the U.S.

Limited movement

While the two countries are keen to trumpet their shared goals on defense, other parts of the relationship will be trickier to navigate. 

Starmer is keen to discuss efforts to tackle illegal migration whenever he meets foreign leaders — as he did when Emmanuel Macron was in town last week — but joint endeavors in this area could prove limited.

The U.K. wants Germany to ramp up prosecution of smuggling gangs on its turf, although the substance of that plan was already agreed between the two interior ministries last year. Downing Street stressed the necessary changes to German law would now be made by the end of the year.

Von Ondorza said that while Merz was more open than Scholz to making migration “a central pillar” of their interactions, it was “less clear” what Britain and Germany could do to help each other on this front compared with France.

Then there is the vexed topic of movement between the two countries. Starmer and Merz are expected to confirm changes which will make it easier for German schoolchildren to visit the U.K. 

A second German official said it was “a tangible result” from bilateral discussions on mobility, while the bigger prize of an EU-wide agreement on students coming to Britain — something Berlin is pushing hard for — is still distant.

Meanwhile, German officials have warned it will still be “some time” before all British passengers are allowed to use e-gates when entering the country — something Starmer hailed as a win from the recent EU-U.K. “reset” agreement. Frequent travelers to Germany are set to gain access to e-gates as an interim step, however.

For now, visits between Berlin and London remain a little easier for Merz and Starmer than for the citizens of the countries they lead.

Sam Blewett and Jon Stone contributed reporting.