Image caption Rob Semple said he was convinced the investigation would be "fair and thorough"

A senior Conservative official has quit his role overseeing the inquiry into bullying within the party, following an investigation by BBC Newsnight.

Newsnight had revealed key witnesses were reluctant to give evidence while Rob Semple was part of the process.

The inquiry was set up after the suicide of activist Elliott Johnson.

Mr Johnson's parents had called for Mr Semple to step down over his links with Mark Clarke, the man at the centre of many of the bullying allegations.

'Establish the truth'

Last year Mr Semple became chairman of the Tory's volunteer organisation, the National Convention, with the strong support of Mr Clarke.

On Tuesday, the parents of Mr Johnson, the 21-year-old Tory activist whose suicide last September sparked claims of unchecked bullying within the party, told the BBC that Mr Semple should remove himself from any involvement in the inquiry, which is being undertaken by the law firm Clifford Chance.

Earlier this week, Mr Semple had insisted he would not step down and was no longer in touch with Mr Clarke, but, in a statement on Thursday, he announced a U-turn.

He said: "As a father myself, the wishes of Mr and Mrs Johnson are paramount to me and, after seeing their interview on BBC TV, I have decided to recuse myself from the board meeting that will discuss the Clifford Chance report.

'Deep reservations'

"As a Conservative volunteer for 20 years, I want to establish the truth of what happened to Elliott.

"I am convinced the investigation will be fair and thorough and my decision must not be regarded as my accepting any suggestion that I would be less than impartial.

"As chairman of the voluntary party, I will be pressing for the implementation of all the recommendations of the investigation."

Image copyright PA Image caption Elliott Johnson was found dead in September

Mr Johnson, whose son Elliott had complained of being bullied before he died, said: "This is a victory for common sense.

"Mr Semple has done the right thing, but I still have deep reservations about this whole process.

"The Conservative Party seems to want to control this process which makes people very suspicious about its motives.

"I still don't believe this is a truly independent inquiry."

15 key witnesses

Fifteen key witnesses to the bullying inquiry had told the BBC they wanted Mr Semple to stand down from any involvement in overseeing the report on the scandal.

A number of them also said they would be reluctant to talk to the Clifford Chance investigation while he was still involved.

The law firm has been commissioned to file a report that will be considered by the Conservative Party board before it is published.

Mark Clarke has always denied any wrongdoing.