Memo said activist was 'sociopathic, dangerous and a bully'
Senior Conservative Party officials received a memo in August which warned the activist at the centre of the Tory bullying scandal was "sociopathic" and "dangerous".
It urged officials to keep Mark Clarke away from the party's youth wing and warned failure could be "devastating".
The memo, obtained by BBC Newsnight, was produced by a then-party staffer.
Mr Clarke has vigorously denied all allegations.
The document suggested that party staff had been aware that Mr Clarke had been "badly behaved" before the May 2015 election, and led Tory chairman Lord Feldman to launch an internal investigation.
Newsnight understands the memo was produced as an aide memoire for a meeting with a party official in which the former staffer made a verbal complaint about Mr Clarke.
In it, the author writes that Mark Clarke's "bullying tactics are well-known… it would literally be impossible to list all his crimes here".
The document does not directly contradict the insistence of party chairman Lord Feldman that he was unaware of Mr Clarke's alleged bullying before August.
However it suggests that numerous complaints about Mr Clarke's behaviour had been made in the months before the young activist Elliott Johnson himself complained about being bullied by Mr Clarke.
Mr Johnson took his own life a month later in September, leaving a letter which named Mr Clarke.
The party has since been dogged by a stream of allegations of bullying, sexual harassment and blackmail by Mr Clarke - and suggestions that Tory bosses should have taken action against him earlier.
In the memo, the former staffer at Conservative Campaign Headquarters (CCHQ) says that Elliott Johnson's complaint "is the tip of the iceberg. Before the election we knew he [Clarke] was badly behaved but he managed to keep it away from us and under wraps. Since then he appears to be unravelling.
"In the months since the election, Conservative Future [the party's youth wing] activists who have come across him have had one of three things happen to them: been bullied, been lied to about his involvement with CCHQ or been hit on."
The former CCHQ employee goes on to say: "I receive I don't even know how many complaints about Mark Clarke and CCHQ's endorsement of him. I feel irritated that no one is stepping up to try and protect these young activists who have just worked bloody hard helping to deliver a majority and deserve thanks - not to be shelved by CCHQ and yelled at by Mark Clarke."
The memo also warns that Mr Clarke is "sociopathic, dangerous and a bully". It was handed in to a senior member of staff at CCHQ on 14 August. It was then passed to Simon Mort, the official initially charged with investigating complaints about Mark Clarke.
It concludes by warning: "At the very least you need to keep him [Mark Clarke] away from Conservative Future as the effect he has could be devastating."
Mr Clarke was not suspended from the party until a month later, following the death of Elliott Johnson.
Mr Clarke was removed from the list of potential Tory candidates in 2010 after complaints about his behaviour during his campaign to become MP for Tooting in south London.
However he succeeded in working his way back into the party machine by launching RoadTrip 2015, an organisation which bussed young volunteers around the country to campaign in target seats.
Former Conservative chairman Grant Shapps, who gave Mr Clarke his backing and an official party role, resigned from his job as an international development minister last weekend.
Speaking to BBC Newsnight, the author of the memo, said that the document was a "brain dump" and not intended for publication.
"I was concerned that Mark Clarke was going round saying that he was to be the Director of 2020 Roadtrip," the staffer said. "People had been told by Mark Clarke, that his directorship had been endorsed by CCHQ. I felt that Mark Clarke shouldn't be let anywhere near CCHQ."
The former staffer told Newsnight that Mark Clarke's behaviour within CCHQ in the run up to the election, was troubling. "I didn't like the way he treated his interns at CCHQ. These young people were here as volunteers, doing unpaid work for CCHQ. Clarke was tough on them. He was abrupt and short."
Ray Johnson, Elliott's father, believes CCHQ knew about Mark Clarke's reputation "but didn't want to rock the boat… I was told that 25 complaints were made about Mark Clarke to CCHQ going back a year."
He continued: "My understanding is that complaints were not treated the way they were supposed to be treated. RoadTrip was a successful campaign vehicle and they didn't want to do anything to jeopardise that. Any complaints were quietly shuffled away."
The author of the memo says party officials responded appropriately to the memo and Elliott Johnson's complaints. The former staffer said: "The weekend after Elliott's complaint was submitted, there was a conference call about it with the top bods from CCHQ. Soon after that, people were being called in to the investigation. Yes, CCHQ were bureaucratic and yes CCHQ were careful and so that may have delayed things. But they certainly cared."
The former staffer was asked to meet Mr Mort in the first week of September, three weeks after handing in the memo: "I wasn't a victim. I wasn't a complainant. He just wanted background."
It's understood the former party worker met Mr Mort on the same day as Elliott Johnson. By then Elliott had been persuaded to retract his own complaint.
A CCHQ spokesperson said on Wednesday night that the memo obtained by BBC Newsnight was part of "a bundle of complaints within one document which CCHQ immediately started to investigate".
She refused to comment on the specific allegations in the document: "An investigation is currently under way and it is not appropriate to comment until we can establish the facts."
Mark Clarke has previously denied all allegations of wrongdoing against him. "I believe that these false allegations and this media firestorm are related to the events surrounding Elliott's sad death," he said.
"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."