The parents of a young Tory activist who took his own life after claiming he was being bullied within the party have said they will boycott an inquiry into the allegations.
Lawyers were brought in to investigate bullying within the Conservative youth wing after Elliott Johnson was found dead on railway tracks within weeks of raising allegations about the way he was being treated.
Parents Ray and Alison said they believe the probe is "biased" and their solicitor has raised concerns about the "lack of independence and transparency".
Party chairman Lord Feldman has faced calls to quit amid claims - which he has denied - that he was aware of bullying within the youth wing.
Former Tory election aide Mark Clarke was expelled from the party last month following allegations of bullying - which he strongly denies.
Mr Johnson told The Mail on Sunday: "We have never accepted Lord Feldman's position that he was 'wholly unaware' of Clarke's behaviour until August - not unless he was deaf, dumb and blind.
"We believe Feldman and other senior officials were fully aware of Clarke's past, but were prepared to allow him to direct the party's campaign and risk the safety of young activists used as mere fodder to achieve electoral success.
"As each day passes we believe it becomes clearer that Tory HQ is complicit in a cover-up to protect its chairman, regardless of the damage it has caused to its youth wing. The party has cleansed its youth wing - the question is now who will move to cleanse Tory HQ itself?"
The Conservatives brought in Clifford Chance to carry out the investigation but the couple said they are boycotting the inquiry because the law firm has failed to satisfactorily answer questions about its links to the party.
In a letter to Clifford Chance, the Johnson family solicitor said: "For all you have told us the Prime Minister could be a client and Lord Feldman good friends with senior partners of Clifford Chance."
Mr Johnson said the Conservative party had framed the terms of reference of the inquiry and believed witnesses could be "questioned in a manner favourable to the Conservative Party, preventing them giving full and frank answers".
He told the newspaper: "We are concerned that the hands of Tory HQ will be pulling the strings from behind the scenes as their actions to date show that they are more interested in protecting the party machine and its staff than in natural justice for Elliott and other young activists."