LONDON — Friedrich Merz will make his first visit to the U.K. as German chancellor on July 17 to sign a landmark treaty with British premier Keir Starmer, according to three people familiar with the plans.

Details of the wide-ranging pact promoting cooperation on defense, economic growth and tackling illegal migration were first reported by POLITICO earlier this week. The treaty is expected to feature a mutual assistance clause specifying a threat to one nation would be regarded as a threat to the other.

Merz’s trip to London caps off nearly a year of talks since Starmer issued a joint declaration with then-Chancellor Olaf Scholz promising closer alignment between the two countries.

Starmer’s team has been courting closer relations with Berlin since they were in opposition, particularly on defense and security, which was the focus of a separate agreement signed last October.

An ally of the German chancellor said that he was keen to put a “personal face” on the U.K.- German relationship.

However, the date of Merz’s excursion was subject to intense negotiations as officials were keen not to detract from Emmanuel Macron’s state visit, two people with knowledge of the process said.

British Defense Secretary John Healey has already established a good relationship with his German counterpart, Boris Pistorius, as the two navigate major reforms to their national armies.

One area of discussion which will be more sensitive is the treaty’s wording on cross-border movement, as Berlin pushes for a new EU-wide agreement on youth mobility while Starmer faces pressure to cut migration.

Chris Lunday and Anne McElvoy contributed to this report.