LONDON — Britain’s chief rabbi chastised the Labour Party on Monday for its handling of anti-Semitism in its ranks, breaking rabbinical convention to join other Jewish institutions in cautioning people against supporting the party in next month’s election.

Jeremy Corbyn, the Labour leader, reacted defiantly on Tuesday night, refusing to apologize in a BBC interview for his party’s response and defending the slow pace of some investigations into anti-Semitic remarks by party members.

The chief rabbi’s rebuke instantly generated fierce debate among British Jews, with some seeing it as reflecting their fears of Labour and others saying that he did not speak for them.

The chief rabbi, Ephraim Mirvis, an Orthodox rabbi who used to lead a North London synagogue, suggested in an article in The Times of London that Mr. Corbyn was “unfit for office.”