WESTMINSTER must adopt a “zero tolerance” approach to sexual harassment, the Commons Speaker has insisted, as MPs heard claims of assault, abuse and bullying on the parliamentary estate.

John Bercow challenged political parties to "live up to their responsibilities" as he called for change at Westminster amid what he described as "disturbing" allegations about a "culture of sexual harassment".

He said Theresa May's call for a Commons-wide mediation service and contractually-binding grievance procedure for MPs and staff should be considered.

But in a statement to MPs, the Speaker stressed: "In the first instance I hope that parties will live up to their responsibilities, demonstrating both an appetite for change and a practical means of delivering that change without delay. Make no mistake, there is a need for change."

During an Urgent Question, called by Labour’s Harriet Harman, Liz Saville Roberts, Plaid Cymru's leader at Westminster, said she knew of a member of Commons staff, employed by an MP, who had reported earlier this year being sexually assaulted to the authorities, “who did nothing”.

Ms Saville Roberts went on: “She is deeply disappointed and distrustful and she tells me distrust is endemic.”

Andrea Leadsom, the Commons Leader, replied by saying if the member of staff wanted to mention the circumstances to her, she would take up the case personally.

Labour’s Chi Onwurah recounted how harassment complaints made against MPs for their actions towards researchers in a parliamentary bar were dismissed as being typical pub behaviour.

The Newcastle MP said she received the dismissive response after raising concerns that a number of male and female researchers had been made to feel "deeply uncomfortable" by MPs in the Sports and Social club at Westminster.

Ms Leadsom, in her reply, made clear she would be holding talks about the parliamentary bar on Tuesday. The Prime Minister sat beside her throughout the Commons exchanges.

Tory MP Matthew Offord said the problems at Westminster were not just about sexual harassment or women but also about bullying, which, he described as “systemic”.

Jess Phillips, the Labour MP for Birmingham Yardley, claimed she heard two male colleagues talking about "a witch-hunt that was going on in Parliament" over the claims of sexual harassment of staff.

Her Labour colleague Lucy Powell urged leaders on all sides of the Commons to take action against their allies "even when that is inconvenient".

Ms Harman, the Mother of the House, insisted no one should have to work in a "toxic atmosphere of sleazy, sexist or homophobic banter".

The former Labour deputy leader called for complainant anonymity to be at the heart of a new system to deal with any allegations of abuse.

"No woman or man, for that matter, coming to work in this House should be subjected to unwanted sexual advances from those who are in a position of power over them,” declared the London MP.

"No MP, let alone a minister, should think it is something to make jokes about. This is not hysteria,” she declared, “this is something which is long overdue for all the parties in this House to deal with."

Ms Leadsom told MPs that the allegations made it clear there was a "vital need to provide better support and protection for the thousands of staff members working in Westminster and in constituency offices across the country".

Parliament has been rocked by allegations involving a string of MPs.

They included Tory Trade Minister Mark Garnier, who the Mail on Sunday reported had asked his female secretary to buy him a sex toy from a Soho sex shop. He is said to have claimed it was 'good humoured high junk' - but a probe has been ordered into whether he broke the ministerial code of conduct.

She said Parliament must establish a House-wide mediation service, complemented by a code of conduct and contractually binding grievance procedure, available for all MPs and peers, and their staff, irrespective of their party banner.

"It is a right, not a privilege, to work in a safe and respectful environment; these plans will ensure that Parliament takes a zero-tolerance approach. Parliament must take action in days, not weeks," she added.