LONDON — Nobody expected Britain’s general election to follow a smooth script, and by the end of a second hectic day of campaigning both of the country’s major parties had suffered a series of unexpected bumps and blows. On Thursday, it was the opposition Labour Party’s turn.

Two former Labour members of Parliament declared that they planned to vote for the Conservative Party because they said Labour’s leader, Jeremy Corbyn, was unfit to be prime minister. Their comments came a day after the sudden resignation of the party’s deputy leader, Tom Watson, who had tangled for years with Mr. Corbyn over Brexit policy and anti-Semitism in the party’s upper ranks.

The upheaval threw Labour’s campaign into disarray only a day after Prime Minister Boris Johnson’s Conservatives stumbled out of the gate. In just 24 hours they were hit with the sudden resignation of one of Mr. Johnson’s cabinet ministers in a legal scandal, an apology from another following widely condemned comments about the Grenfell Tower fire and accusations that the party had doctored a TV interview with a prominent Labour politician.

In Labour’s case, the internal dissent resurfaced allegations of anti-Semitism that have long haunted the party.