Sir Keir Starmer has refused to give more information about why Louise Haigh resigned as transport secretary last week.
Haigh stepped down after it emerged she had pleaded guilty to a fraud offence a decade ago, a conviction she reportedly told Sir Keir about in 2020, when he appointed her to his shadow cabinet.
During Prime Minister's Questions, Conservative leader Kemi Badenoch asked why the prime minister had appointed a "convicted fraudster" as his transport secretary.
Sir Keir said Haigh had been right to resign "when new information came to light".
But, when asked by Badenoch for details about the new information, he replied: "I'm not going to disclose private information."