U.K. Prime Minister Keir Starmer and German Chancellor Friedrich Merz are set to sign a treaty on Thursday pledging to tighten defense ties and step up law-enforcement cooperation against gangs that smuggle migrants across the English Channel.

The center-right German leader is in London on his first official visit to Britain since taking office in May. Starmer visited Berlin in August 2024, announcing plans for the U.K.-Germany "friendship and cooperation" treaty with Merz's predecessor, Olaf Scholz.