The European Union should offer Britain “privileged third-party status” in defence and foreign policy cooperation after Brexit, the German defence minister, Annegret Kramp-Karrenbauer, has said in a speech in London.

She said that such status should include access to projects such as Future Combat Air System, the Franco-German stealth jet programme.

Her remarks – following a meeting in London with the UK defence minister, Ben Wallace – underline how determined the major European powers are to ensure that they do not lose the UK’s defence assets after Brexit.

“I am convinced the UK has to be a privileged third party in our German and EU cooperation as a third party,” she told an audience at the London School of Economics. She also stressed how much Germany welcomed the rapidly developing format of the “EU 3” – Germany, France and the UK – cooperating over defence and foreign policy, citing the recent examples of Iran, where the three have tried to keep the nuclear deal intact despite the US’s withdrawal, and Libya. The format, she said, was very effective. She stressed, for instance, that the EU could not allow Russia to determine the future of Libya when issues of migration from the country would affect Europe and not Moscow.

Her remarks are not only significant because she is German defence minister, but because she has been chosen as chair of the CDU, and the party’s preferred choice to succeed Angela Merkel as chancellor.

Once the UK leaves the EU at the end of January, it will no longer be entitled to attend EU foreign ministers’ meetings or discussions on future defence cooperation. Brexit also raises questions of whether the UK will have access to the European Defence Fund or be able to cooperate on joint EU defence projects.

Kramp-Karrenbauer said she would even like to see the UK’s involvement in the European fighter project FCAS. However, she saw any strengthening of the European defence pillar as taking place within Nato structures. These remarks also put her at odds with the French president, Emmanuel Macron, who has described Nato as “brain dead”.

She said although reliance on US defence forces in an era of Donald Trump was less plausible, she said the EU simply did not have the assets to operate independently of the US at this stage: “We cannot rely on the fact that our interests are going to be considered by the US as much as they used to be.” She added that not every proposal from Macron to reform the EU was in the German national interest.

There are British hopes that with Germany holding the EU presidency in the second half of next year, German leadership may help the UK secure a closer economic relationship. But she warned that a trade deal will be harder to secure than defence cooperation, and that there could be no question of cherry-picking.

She also described Brexit as a tragedy, saying it hurt the UK, Germany and the EU, and added that a huge amount of energy was being expended that could have been directed elsewhere. “Things that belong together are being ripped apart,” she said.

She also praised Prince Harry’s enthusiasm after she met him to discuss the German plan to host the next Invictus Games in Dusseldorf.