Jewish Conservative politician Grant Shapps has resigned following claims he failed to act on allegations of bullying within the party.
The accusations surfaced after the apparent suicide of a Tory youth activist in September.
The alleged bullying took place while Mr Shapps was co-chair of the party. In a letter to the prime minister last week, he wrote: "Over the past few weeks - as individual allegations have come to light - I have come to the conclusion that the buck should stop with me."
Youth organiser Mark Clarke has rejected allegations of bullying, sexual assault and intimidation.
The scandal has engulfed other leading Jewish Conservative politicians - Lord Feldman, the party chairman, and his deputy Robert Halfon.
Reports suggest that the decision to give Mr Clarke a leading role in campaigning was approved by the Tories’ senior management, including Mr Shapps and Lord Feldman, last year.
Potters Bar and Brookmans Park Synagogue member Mr Shapps was a Foreign Officer minister.
Critics have claimed he knew about the allegations around Mr Clarke before giving him a bigger role, but sources close to Mr Shapps are said to have denied he knew about the extent and nature of the complaints.
Earlier this month it was claimed that Mr Halfon was the subject of a blackmail plot which emerged as he admitted to a relationship with a Tory campaigner.
Mr Halfon, the former political director of Conservative Friends of Israel and the descendant of Libyan Jews, was reportedly filmed as he left a private members’ club with the woman.
One of the complaints against Mr Clarke was that he had allegedly attempted to mastermind one or more blackmail plans. He denied any role in the episode involving Mr Halfon.
Lord Feldman, a close friend of David Cameron and supporter of a range of Jewish charities including Jewish Care, is now responsible for overseeing the investigation into the allegations against Mr Clarke.
The peer has asked a partner at the Clifford Chance law firm to run the probe.
Mr Clarke was expelled from the party for life last week. He denies all claims of wrongdoing.
The Conservative Party has said it cannot comment on the matter until the investigation is completed.
To get more news, click here to sign up for our free daily newsletter.