LONDON — The question, from a student in a university lecture hall, is one that Keir Starmer hears virtually every day about Britain’s decision to withdraw from the European Union, or Brexit.

“I feel, like many others of the 48 percent, abandoned and leaderless,” protests the questioner, referring to those who voted to remain in the bloc in last year’s divisive Brexit referendum.

For Mr. Starmer, who speaks for the opposition Labour Party on Brexit, replying means walking a familiar tightrope. With Labour having consented to the plebiscite, he says, it would be intellectually dishonest to say, “Now it’s gone the way I don’t want, so I’m not going to accept the result.”

Then comes the counterpunch: “I don’t give up on any of the values that made me want to remain,” he tells the 40 or so students sitting in a semicircle around him, calling for a relationship with the bloc “based on a progressive partnership.”