LONDON — Volodymyr Zelenskyy met with British Prime Minister Keir Starmer on Saturday as European leaders grapple with the fallout from an extraordinary on-air exchange in which the Ukrainian president was loudly berated by Donald Trump.

Ahead of the meeting, Starmer told Zelenskyy, “We stand with you, with Ukraine, for as long as it may take. And I hope you’ve heard some of that cheering in the street that is the people of the United Kingdom coming out to demonstrate how much they…