The handling of allegations of bullying and blackmail by a senior Conservative aide must be the subject of a fully-independent inquiry, the former head of the party's voluntary wing said.
Emma Pidding - who denies any wrongdoing during her tenure as chair of the National Conservative Convention - warned any internal investigation into Mark Clarke "will lack credibility".
The prominent activist - who was awarded a peerage this year by David Cameron - backed a call for an independent probe by the parents of activist Elliot Johnson who killed himself, leaving a note accusing Mr Clarke of bullying.
Senior Conservatives are meeting over the handling of the allegations, which Mr Clarke denies, as pressure mounts on party chairman Lord Feldman to quit.
Grant Shapps, who was co-chairman with Lord Feldman until the general election, resigned as International Development Minister at the weekend, telling Mr Cameron the buck stopped with him.
The father of Mr Johnson had called for both to go.
Downing Street has stressed that Lord Feldman - who chairs the Conservative Party board which is meeting to discuss the issue - retains the "full confidence" of the Prime Minister.
But a senior Tory source confirmed the peer is among 40 "witnesses" who are giving written evidence to party officials.
The peer is understood to have launched the investigation into the allegations surrounding Mr Clarke in August, but has never played a part in it.
In a statement published by the ConservativeHome website, Baroness Pidding said: "Events over the past 48 hours have made it clear any investigation organised by the Conservative Party into its own handling of this sorry affair will lack credibility.
"At the heart of this, we are talking about the tragic and needless death of a young man who lived for our Party. I have come to the conclusion his parents are right in saying any inquiry must be entirely independent of that Party.
"Otherwise I do not believe the public at large will trust the outcome."
Baroness Pidding dismissed reports that she may have released details of complaints made against him to Mr Clarke.
"I have already made it clear that allegations made against me are false. I am hiding nothing and I am quite happy to answer any questions an independent inquiry may put to me," she said.
"I believe it is time for the Conservative Party to be put up to the same level of scrutiny."
The final straw for Mr Shapps appears to have been the emergence of an email sent to him by ex-minister Baroness Warsi in January, complaining that the election campaign aide had been abusing her on Twitter.
The party had previously insisted that no complaints against Mr Clarke, who ran its RoadTrip canvassing drive in the run-up to the election, were received before August. He has since been expelled from the party.
Law firm Clifford Chance LLP has been instructed to prepare a report on the issues raised, with a remit to assess whether complaints were handled properly and "identify any individuals who were at fault".
The firm's lawyers will also consider the integrity of the evidence-collecting process and whether the right people have been interviewed.
The collection of evidence is not expected to be completed until the end of the year, and Clifford Chance will produce the report "as soon as possible after that".
The source added: "It will be a decision of the board which parts of the report to publish having regard to protecting vulnerable witnesses, the ongoing coroner's inquiry and police investigation. Subject to this, the party intends to publish the key findings and recommendations."
Tory MP Charles Walker, a member of the party board, told the Guardian it would be "deeply, deeply concerning" if complaints had been made that were then leaked to Mr Clarke himself.