A Conservative MP says party bosses failed to act on multiple complaints and warnings about bullying, harassment and blackmail by a senior activist.
Ben Howlett told BBC Newsnight there was "institutionalised bullying" in the party's youth wing, after he stepped down as its chair in 2013.
Allegations of inappropriate behaviour by Mark Clarke, who ran a campaign bussing volunteers around the country during the election, surfaced after Elliott Johnson, a young party activist, took his own life in September.
After it was approached by Newsnight for comment this week, the Conservative party said it was banning Mr Clarke, who denies the claims, for life.
After Mr Johnson's death, it emerged that he had complained to Conservative Central Office that Mr Clarke, a former Conservative parliamentary candidate, had threatened to destroy his career. He also named Mr Clarke in a letter found by his parents.
Ben Howlett, MP for Bath, told Newsnight he first raised concerns about Clarke's behaviour with party bosses in 2010 and had discussed Clarke with current party chairman Lord Feldman and Baroness Warsi, chair from 2010 to 2013.
Newsnight has spoken to five more activists who say they made complaints about Clarke before Johnson's death.
Mr Howlett said: "We've complained about him [Clarke] for a long period of time, and it's not just him, it was people that were attributed to him as well.
"I complained when I was national chairman directly to Sayeeda Warsi as the party chairman, I complained directly to the chairman's office when Grant Shapps took over as the party chairman and I have to say Lord Feldman has been well aware of all this, for a very long period of time."
Asked about Mr Howlett's claims, the party said Lord Feldman was not aware of allegations against Clarke until August 2015 when he "acted immediately to set up an internal disciplinary inquiry".
A Conservative spokesperson said on Tuesday night: "We have been checking and rechecking, but have not been able to find any records of complaints that were made but not dealt with - but we are determined to get to the bottom of what's happened."
Mr Clarke ran RoadTrip, an organisation which bussed young volunteers, largely drawn from Conservative Future, around the country to help campaign in marginal seats.
Howlett says his complaints about Mr Clarke were not investigated. He says it was "water off a duck's back, ignore it, move on".
He said he had suffered mental health issues as a result of his own bullying by Clarke and had heard a "huge range" of complaints from others, including women complaining about sexual advances by Clarke.
Mr Howlett said the party had failed to confront what he described as "institutionalised bullying" within Conservative Future after 2013.
"It was unfortunately swept under the carpet in the big scheme of things, because the party didn't want to end up having the general election result lost I can imagine, and you don't want to talk about those kind of thing whilst an election is going on."
Since learning of Newsnight's allegations, the Conservative Party has said it will no longer recognise RoadTrip as an official Conservative campaigning body.
The circumstances around Mr Johnson's death are the subject of both a coroner's inquiry and a police investigation. The party says it is passing all complaints about Mr Clarke to police.
One former activist told Newsnight Mr Clarke had sexually harassed and then threatened her, telling her he had a dossier of information on her sex life.
"He pointed out that he knew that I was quite outspoken, that he'd seen me criticising certain things that the party was doing - certain campaign things - and that I should be on board and that I could have all of these favours, they could do all these great things for me if I joined them.
"At that point he tried making a move on me and I backed away. He stroked my arm and tried to put his hand up my skirt and I backed off and said I don't want any part of this. Get off me basically."
After the incident, she said: "He sort of said: 'If you're not one of us, we can destroy you basically, we will destroy you. If you try to take us on we will ruin you. We'll make sure that you don't have any kind of career in public affairs or in Parliament.'"
The woman complained to Conservative Central Office in the summer of 2014 that he had attempted to blackmail her when she refused his advances. She says she received an acknowledgment of her complaint but heard nothing more.
Ray Johnson, Elliott's father, said: "I find it staggering if Ben Howlett MP has come out and damned Feldman and Shapps for not having acted. If this turns out to be true Lord Feldman and Shapps should look to their consciences and resign immediately."
Mr Clarke told Newsnight he strongly refuted all allegations of bullying, harassment, assault or attempted blackmail.
He said: "I believe that these false allegations and this media firestorm are related to the events surrounding Elliott's sad death. As such I will be co-operating with the coroner and providing him with the fullest information. This is the proper process. After the inquest I will look to take legal action for defamation in respect of these allegations."
More on this story on BBC Newsnight at 22.30 GMT on Wednesday on BBC Two. You can catch up afterwards on iPlayer