Senior figures in the Conservative Party had planned to gather in Manchester’s Midland Hotel on 4 October for a triumphant “leaders’ reception” to celebrate the work of one of its key campaigns. The event’s organisers had boasted that the Prime Minister would be guest of honour after the opening day of party conference.

But now the RoadTrip 2020 reception has been cancelled, the group’s Facebook page has been deleted, and the project, which had David Cameron’s backing and had mobilised thousands of campaigners before the election, faces an uncertain future. Allegations of bullying inside the team, which have sent shockwaves through its activist and youth ranks, are taking their toll.

Mark Clarke, RoadTrip’s founder and director, who is a former Conservative parliamentary candidate, has been banned from the conference alongside two other activists who are also members of Conservative Future, the party’s youth wing. One individual, reported to be Mr Clarke, has also been suspended as a party member pending the outcome of a disciplinary inquiry.

Mr Clarke, 37, himself a former chair of Conservative Future, became known as the “Tatler Tory” in 2008 when the society magazine tipped him as a future cabinet minister. But he began working as an organiser after narrowly losing his bid to become MP for Tooting to the Labour incumbent Sadiq Khan in 2010.

Mr Clarke is at the centre of the allegations of bullying reportedly made by Elliot Johnson, a Tory campaigner and journalist whose body was found on railway tracks in Bedfordshire on 15 September. It is understood that more than two dozen complaints have been made to the Conservative Party by young activists.

Mr Johnson, a 21-year-old member of Conservative Future and a former online journalist at Conservative Way Forward, a campaign group, complained about alleged bullying before he died. British Transport Police has confirmed that it is preparing a file for the coroner following the bullying claims. Mr Johnson’s death itself is not being treated as suspicious.

In a statement to The Independent, Mr Clarke said: “I strongly refute any suggestion of bullying or harassment. I am not making any further comment about this matter. The family have asked for privacy and I respect their wishes and the coroner’s process.”

Friends of Mr Johnson are preparing to remember him in a pub in Manchester on 3 October. They describe him as a dedicated, loyal and talented young activist. “He loved the party,” one friend said. “It was like his family. He was very enthusiastic and really got caught up in the excitement of the election campaign.”

The events have shocked the party and its campaigning base, triggering calls to improve the protection of young people under the Conservative umbrella on the eve of its first conference since election victory last May.

“In politics there is a difference between bullying and what you expect when you put yourself in the limelight,” says Liam Walker, 24, chairman of Conservative Future in Witney, the Prime Minister’s constituency in Oxfordshire. “There needs to be more of a support network in place. People don’t know where to go or what to do if they feel like they are being bullied.”

A spokesperson for the Conservative Party said: “We are taking our ongoing internal inquiry extremely seriously, and we need to establish all the facts. As such, we cannot say anything further at this time.”

The party said that the inquiry had begun “as soon as a complaint was received in August 2015”, before Mr Johnson’s death, and confirmed that three people had been banned from the conference and that “an individual has had their [party] membership suspended, pending the outcome of a full disciplinary panel”.

A Conservative insider who wished to remain anonymous said that the effects of a new, increasingly centralised approach to party politics had filtered through the ranks. “I don’t think that was the intention but it is the result of disenfranchising the voluntary party and putting more power in the hands of central office.”

Local constituencies have increasingly faced impositions from party headquarters, including the controversial “A-list” of preferred candidates originally conceived after Mr Cameron became party leader in 2005. RoadTrip 2015 was a function of centralised campaigning. Under Mr Clarke’s direction, and as a key cog in then party chairman Grant Shapps’s “Team 2015” machine, the project involved bussing hundreds of activists across the country between target seats.

Activists, many of them drawn from Conservative Future, were rewarded with nights out and photo opportunities. The project’s detractors labelled it “ego trip” but supporters credited it with energising the Tory faithful and reaching more swing voters with more vigour than local associations could muster.

After the election, Mr Clarke re-emerged as the director of RoadTrip 2020 and quickly won renewed senior backing, including from the incoming party’s vice-chairman Robert Halfon. Baroness Pidding, a veteran campaigner and the former leader of the party’s National Convention, became the group’s chairwoman. In July, Lady Pidding, who was made a life peer by Mr Cameron in August, shared a platform with Mr Clarke and the Prime Minister at the annual meeting of the National Convention in London. Lady Pidding declined to comment on 2 October.

The bullying investigation, which is being overseen by the Conservative Party chairman Lord Feldman, comes as Jeremy Corbyn acknowledged this week there was a problem with an online culture of abuse in Labour’s ranks. This came after Yvette Cooper, who had challenged Mr Corbyn for the leadership, warned its women’s conference of the effects of “abuse, harassment, bullying and misogyny in politics”.

In 2014, the Conservative Party issued a voluntary code of conduct for MPs after a survey of parliamentary workers, conducted as part of a Channel 4 News investigation, revealed a culture of bullying and sexual harassment in Westminster, particularly against young men. The Conservative Party did not respond to questions about what systems it had to protect the welfare of volunteers and activists.