A former parliamentary staff member has described how "physical, emotional and psychological abuse" by the MP he worked for left him a "broken shell of the young man I once was".
Peter Bone was suspended as a Conservative MP after an investigation found he had bullied and was sexually inappropriate around the individual.
The MP's ex-assistant told the BBC the experience led to him being diagnosed with post-traumatic stress disorder.
Mr Bone has denied the allegations.
In an exclusive interview with the BBC, the ex-staff member said he was also left in "limbo", after a complaint to the Conservative Party was left unresolved for more than four years.
Earlier this month, a separate investigation by Parliament's behaviour watchdog, the Independent Expert Panel (IEP), found the MP for Wellingborough broke sexual misconduct rules by indecently exposing himself to the staffer during an overseas trip.
It also upheld five allegations of bullying, including verbally belittling him, physically striking him and throwing things at him.
Mr Bone appealed against the investigation's findings, arguing it had been flawed. However, his appeal was dismissed.
The watchdog recommended Mr Bone should be suspended from the House of Commons for six weeks.
In response, the Conservative Party withdrew the whip, meaning Mr Bone is now an independent MP.
The suspension is due to be voted on by MPs later.
If approved this would trigger a recall petition and could lead to a by-election in Mr Bone's constituency of Wellingborough in Northamptonshire.
A by-election must take place if 10% of voters in the constituency sign the petition.
'Brutal experience'
The BBC is not identifying the former parliamentary assistant due to the nature of the allegations.
"Peter's behaviour was erratic. His temper was often explosive," he said.
"Like a pendulum he would go from one type of kind of personality to another. It was very hard to predict, and that kind of left me feeling quite under siege.
"They call it a siege mentality in terms of the relentless shouting, the screaming, the hitting."
He added: "My mind and my body were just constantly on edge... That had a big impact on my life at the time, and unfortunately continued to do so for many years afterwards."
The former staff member said the "horrid, brutal, dark experience", which took place more than 10 years ago, "left me a broken shell of the young man I once was".
'Dismissive' response
In September 2017, the individual made a complaint to the Conservative Party.
The investigation progressed for just over a year, with a panel agreeing that there was a "potential breach" of party guidelines and that the complaint should be subject to a further hearing.
But it would be three years until the former staff member heard from the party again - during which time he says he "continually chased", but received a "dismissive" response.
"I was never given a clear timeline of events or even an estimated one," he said. "I was left in this kind of limbo."
The former staff member said he felt there was no urgency from the party and he eventually lost faith in the process.
"I was effectively ghosted for three years by the party," he added.
After waiting almost three years, he submitted a formal complaint to Parliament's Independent Complaints and Grievance Scheme (ICGS), which was formed in 2018 to tackle misconduct by MPs.
Only after the ICGS contacted the Conservatives did the party investigation seem to revive, with the former staff member confirming in March 2022 that he still wished to proceed.
But in July 2022, despite the ongoing investigation, Mr Bone was promoted by Boris Johnson to the role of deputy leader of the House of Commons - a decision the former staff member described as "deeply disrespectful".
It happened the day after Mr Johnson had to resign as leader of the Conservative Party, although he remained prime minister for another two months while the Tories chose his replacement.
His resignation came amid concerns about how he had responded to allegations about another Tory MP, Chris Pincher, who was also subject to a complaint about his behaviour at the time of his promotion.
The former staff member said he was "shocked" but not surprised by the move.
"It's politics, it's a lack of care or empathy," he said.
"Peter was a strong supporter of Boris Johnson... I believe it was purely self-serving. I don't believe they thought about me."
Mr Johnson did not respond to a request for comment.
By August 2022, the Conservative Party had set up an oral hearing. But the complainant was told it would be "adversarial", and involve being cross-examined by Mr Bone - a process he was not willing to take part in.
He withdrew from the process, which allowed the ICGS to proceed with its investigation instead.
"No victim or anyone who makes allegations of abuse should ever have to sit in front of and especially not be questioned by someone who has sexually harassed them, let alone physically, emotionally harassed them," he said.
"Just the idea of it was unbearable."
A Conservative spokesperson said the case was investigated under the party's previous code of conduct and complaints process, "however, the complainant withdrew from the process before the case was heard".
"Under the current process, the complainant's case would have been referred to the ICGS as it is a workplace matter, not a party matter," they added.
They said the process was, by default, adversarial, however, the panel's chair could amend that process where appropriate.
They added that as the complainant withdrew from the process, the case never reached a stage where the chair could make this decision.
The spokesperson said the 2019 general election, the Covid pandemic and less resources devoted to complaints contributed to delays to disciplinary processes during the period in question.
However, they said resources for the complaints team had since increased and processes had been reviewed.
'Relieved'
In a statement following the publication of the watchdog's findings, Mr Bone said the allegations were "false and untrue".
He has not responded to the BBC's request for comment on the complainant's interview.
The former staff member said he felt "relieved" by the findings, but that he hoped it would also lead to more independent oversight of political parties.
"Nothing is ever really going to feel like enough in terms of what was taken from me, my career, my dreams, who I was before I worked in Parliament," he said.
"I haven't pursued this just for myself, I've pursued it for others who have suffered similar abuse, whether it be in Westminster, or in other bodies, who haven't been able to... bring what happened to them to light."
