The Conservatives have been accused of a "whitewash" following the investigation of a party activist at the centre of bullying allegations.

Law firm Clifford Chance found the so-called "Tatler Tory" Mark Clarke was appointed to a key role in the party's general election campaign despite warnings of his past record of "aggressive" conduct.

It found that complaints were made about the conduct of Mr Clarke on seven occasions before the party finally mounted an investigation into his behaviour.

The report said the party's then co-chairmen Lord Feldman and Grant Shapps had not been made aware of the allegations until August last year when an internal party inquiry was launched.

It noted Mr Shapps had seen an internal party report which referred to Mr Clarke's past "aggressive and bullying conduct" when he appointed him to head a Conservative youth campaign drive.

The law firm was brought in to investigate last December, three months after the suicide of a young activist Elliott Johnson, whose complaint against Mr Clarke finally triggered the internal investigation.

In response, the party said it was establishing new procedures for handling complaints by volunteers, including a dedicated hotline and training for relevant party employees.

But Ray Johnson, the father of Elliott, t old Channel 4 News: " We knew in our hearts it would be nothing more than a cover-up. They've exonerated themselves."

Mr Johnson and his wife informed Clifford Chance through their solicitors that they did not wish to participate in the inquiry as it did not appear to be "independent or transparent".

He told the BBC Two Newsnight programme: "We saw it as a whitewash from the start."

Mr Johnson added: " Our view was that they simply wanted to use us as some kind of cover, you might say, some sort of gloss over the inquiry. We weren't prepared to be used as a tool in that way."

Party chairman Sir Patrick McLoughlin said there could be "no place for bullying behaviour" in the party.

"The actions we are taking today will continue to ensure that volunteers, who are so vital to our party, can flourish," he said

Mr Clarke, who has always denied the allegations against him, was appointed by Mr Shapps to lead the party's RoadTrip campaign - taking young activists around the country in support of Conservative candidates - in June 2014.

The report said 13 individuals had been identified who were alleged to have been victims of bullying and harassment or other "inappropriate conduct" by Mr Clarke between January 2014 and August 2015.

In six cases, it was unclear whether any complaint had been made to Conservative Campaign Headquarters (CCHQ) while in seven it was "debatable" whether the alleged conduct amounted to bullying, harassment or other inappropriate behaviour.

However, in four instances it was clear the claims did amount to bullying, harassment or inappropriate behaviour towards young party members and that they had been reported to CCHQ.

Although Mr Shapps's chief of staff Paul Abbott was aware of the allegations, they were not referred to the secretary of the Conservative Party Board's disciplinary sub-committee, Stephen Phillips, and no investigation was carried out.

Mr Abbott did inform Mr Phillips of a complaint about the "general conduct" of people on RoadTrip events - including allegations of sexual assault involving two people unconnected with Mr Clarke - but again there was no investigation as it proved impossible to arrange a meeting with the complainant.

In addition, the report said six specific allegations of "sexually inappropriate behaviour" by Mr Clarke had been identified, including claims that he had propositioned activists or tried to kiss them - but in five cases they were not reported to CCHQ at the time.

In the sixth case, a whistleblower claimed to have lodged a complaint with CCHQ but after no evidence could be found to support that claim the activist concerned stated they wished to withdraw their evidence.

The report also disclosed that when Mr Shapps and Mr Abbott interviewed Mr Clarke to head RoadTrip they had been aware of a confidential file held by CCHQ from the time he was a Tory candidate in the 2010 general election which included reports of "aggressive and bullying conduct" towards his campaign director as well as "negative media coverage" about his activities.

Mr Shapps said he had spent "about 10 minutes" reviewing the file and during the course of the interview told Mr Clarke that it made "very chequered reading".

"Mr Clarke claimed that he had settled down and wanted a second chance to get back on the candidates list," the report said.

"Mr Abbott believed him and Mr Shapps thought he had presented a very compelling case. His work on RoadTrip was discussed as a means of proving himself in this regard."

Mr Clarke refused to be interviewed by Clifford Chance, although his solicitors told the inquiry he was continuing to co-operate with the police and coroner investigating Mr Johnson's death.

"The police investigation into Elliott Johnson's death and other inquiries are ongoing, and it is not appropriate to respond to allegations until the end of those processes," the solicitors said.

"However, the allegations made against Mr Clarke in the Clifford Chance report are wholly untrue and unsubstantiated. Many are based on totally fabricated media reports. All these allegations are vehemently denied."