Tory chairman Lord Feldman was handed a dossier detailing a culture of bullying within the Conservative Party's youth wing in 2010, according to a former activist.
Two people involved in producing the document claimed it named Mark Clarke, an activist expelled from the party last month following allegations of bullying, which he strongly denies.
Lord Feldman insisted that he had not been made aware of allegations about Mr Clarke's behaviour until August 2015.
The party chairman, a close friend of David Cameron, has come under pressure since Ray Johnson, the father of a young activist who apparently committed suicide, called for him to quit.
Elliott Johnson, 21, a member of the Conservative Future youth wing, was found dead on railway tracks in September.
A month earlier he had alleged bullying and his death sparked an investigation and the resignation of former party chairman Grant Shapps.
His father called for Lord Feldman to follow Mr Shapps, claiming "in my mind the tragedy rests on his shoulders".
BBC2's Newsnight reported that the 2010 dossier was given to Lord Feldman by Ben Howlett, who is now a Tory MP.
Patrick Sullivan, who now runs a right-of-centre think-tank, said hard copies of the 2010 dossier were handed to Lord Feldman and then Tory co-chair Baroness Warsi.
Mr Sullivan told Newsnight that Mr Howlett decided to tackle widespread bullying within the party's young activists after being elected to a second term as chair of Conservative Future, the party's youth wing, in 2010.
Mr Sullivan said: "He had a strong anti-bullying stance in the campaign because there had been a culture of bullying. As soon as he was elected, Ben and myself helped compile a dossier and that dossier was given by Ben to Lord Feldman and Sayeeda Warsi."
He added that there had been complaints about Mr Clarke even before 2010, when he was removed from the party's list of approved candidates after a failed campaign in Tooting.
"The dossier is not the only thing," Mr Sullivan told Newsnight. "There were complaints about Mark Clarke in 2008. So complaints about Mark Clarke had been something that Conservative Central Office have known about for a very long time."
Lord Feldman said: "I was wholly unaware of allegations of bullying and inappropriate sexual conduct by Mr Clarke prior to August 2015. Such behaviour is abhorrent to me and had this been brought to my attention I would have taken immediate action to investigate, as I have done since I received the complaint in August 2015."