The roles of three leading Jewish Conservative figures could prove crucial to an ongoing investigation into allegations of a bullying culture within the party.

Conservative Party chairman Lord Feldman, his deputy Robert Halfon, and former chair Grant Shapps are all involved in a row over the sex and blackmail scandal .

There is mounting pressure on the Tories to get to the bottom of the allegations against former party activist Mark Clarke. He ran a leading campaign during this year’s general election, but is the focus of more than two dozen complaints about his behaviour from former colleagues.

The actions of Mr Clarke, who denies any wrongdoing, are said to have been a factor in the suicide of another young party activist earlier this year.

Reports of the row that has now engulfed senior echelons of the party 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 is now 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 denies all allegations of wrongdoing. He was expelled from the party for life last week.

The Conservative Party has said it cannot comment on the matter until the investigation is completed.