The Commons will vote next week on extending investigations into bullying and harassment by MPs to cover historic allegations after an inquiry reported harrowing details of staff being shouted at or groped, and having heavy office equipment thrown at them.

While the government stressed that the vast majority of MPs did not abuse employees, an official report by barrister Gemma White QC recommended that parliament adopt new employment measures to better protect staff.

One of White’s findings was that former members of staff with grievances should be allowed to make historical complaints against members of parliament. The current system only covers events after the 2017 general election.

Following the publication of the report the leader of the Commons, Mel Stride, announced a debate and vote next Wednesday on modifying the remit of the new Independent Complaints and Grievance Scheme (ICGS).

He said one of the proposed changes would be to extend the system to earlier complaints, which was also recommended by a report into bullying and harassment in parliament by Dame Laura Cox last year.

White’s 55-page report concluded that employees of MPs are in a vulnerable position because they are directly employed and consider any form of complaint as “career suicide”. They also often have strong party and personal loyalties which constitute significant barriers to complaint.

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The report detailed examples of persistent bullying. One employee told White the MP they worked for “would intimidate, mock and undermine me every day, often shouting at me”, a regime that left them uncertain and frightened.

They said: “I don’t think of myself as a particularly soft individual, but there were occasions I found myself crying on the way to work, the only time I have cried since I was a child.”

Another staff member told White they were “repeatedly bullied and harassed by [the MP] in a way that had a significant impact on my mental health, eventually leading to my resignation”.

Elsewhere in the report, White wrote: “Some contributors who reported shouting and screaming also reported being present when objects (usually pieces of office equipment, sometimes heavy) were thrown in anger by their employer MP, in some cases at them.”

White said that she also received detailed contributions from individuals who described specific experiences of harassment from MPs, including a serious sexual assault. One staff member described how senior MPs’ staff used parliament’s bars to meet young men and women “in the hopes that we will have sex with them to further our careers”, but that he would would “never in a million years” make a formal complaint as this would wreck his career.

He said: “As things stand now, sexual harassment is just something young working-class people with no connections have to tolerate because networking in parliamentary bars is our only route to a permanent role.

White wrote that unwelcome sexual advances from MPs were often accompanied by attempts at kissing and unwanted touching. “For example breasts being grabbed, buttocks being slapped, thighs being stroked and crotches being pressed/rubbed against bodies. Most of these experiences were isolated, but some were part of a course of conduct on the part of a member or fellow member of staff,” she said.

Figures show parliamentary helplines for bullying and sexual misconduct have received more than 200 calls or emails from staff in each of the last three quarters. However, White’s report shows few MPs have sought help or retraining.

Only 34 out of 650 MPs and 135 out of 3,200 MPs’ staff have attended or signed up to the “valuing everyone” training, designed to support the new behaviour code introduced in July 2018, the report shows.

The report calls for a fundamental shift away from regarding MPs as “650 small businesses” with near complete freedom regarding staff.

In a new development, the report calls for each member to be required to adopt and follow employment practices and procedures aligned with those followed in other public sector workplaces.

“This shift must be supported by a properly resourced and staffed department within the House of Commons. It should develop and implement a coherent and robust approach to members’ employment practice and provide support to members and their staff,” the report says.

Responding to the report, Stride argued that it was necessary to keep the scale of the problem in context. “I say this as a father of three daughters – any one person who is put into a position where they are preyed upon by somebody in authority is one too many, and this needs to be stamped out – there is absolutely no place for that.

“It’s important nonetheless to recognise that the vast majority of members of parliament here will be horrified by some of the things that have surfaced in the report.”

Downing Street described White’s report as “deeply worrying”. The prime minister’s official spokesman said: “It is important that the parliamentary leadership now responds fully and promptly to the concerns raised in this deeply worrying report.”