The Westminster sexual harassment scandal has deepened after it was claimed authorities in Parliament failed to deal with an assault allegation made by a woman working for an MP – despite her reporting it four times.

The female staffer who suffered the alleged sexual assault confided it to another MP, who on Monday exposed the situation during a House of Commons debate.

A different MP said instances of sexually inappropriate behaviour towards young workers had been disregarded by the authorities, while a senior backbencher claimed attempts to strengthen protections for Commons workers had been blocked by political parties.

Minister Mark Garnier, who has already admitted asking his secretary to buy sex toys and to referring to her as “sugar t*ts”, looked set to lose his job after Theresa May refused to say she had confidence in him.

Leader of the House Andrea Leadsom said MPs risk losing their ministerial roles and losing the party whip as a consequence of harassment allegations, even if their behaviour falls significantly below “criminal activity”. Both Commons Speaker John Bercow and Ms Leadsom vowed to take further action, as a list of 36 Conservative MPs subject to allegations of bad behaviour was drawn up by staffers and leaked.

But it was in the Commons chamber on Monday evening that the new allegation of an assault emerged, as the growing scandal looked set to dominate the week in politics.

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Liz Saville Roberts MP told colleagues: “A worker employed as staff of a Member in this House told me today that she reported being sexually assaulted to the proper authorities earlier this year, who did nothing. She is deeply disappointed and distrustful and she tells me that distrust is endemic. How can I assure her that her complaint will now be treated differently?”

The Plaid Cymru member later told The Independent the victim had been so incensed at the assault and lack of an adequate response, that she reported it to the authorities four times in the hope action would be taken.

In the end she was told to go to the police, but when she did the case was not taken further.

Ms Saville Roberts told The Independent: “You would expect this place to be setting an example and not lagging behind what is normal workplace practice anywhere else in the country.”

Ms Leadsom said in the chamber that she would personally listen to the woman’s allegation and deal with it herself, but the problem of inappropriate behaviour was also reported by others.

Labour Newcastle MP Chi Onwurah told of instances she had heard of that took place in the Sports and Social bar in the Palace of Westminster, a place where young staffers and MPs can regularly be found drinking in the evening.

She said : “When I complained recently to an officer of Parliament who had some responsibility in this area, that I knew a number of researchers, male and female, who had been made to feel deeply uncomfortable in the Sports and Social club here, by Members of Parliament, I was told that that happens in pubs all over the country.”

Jeremy Hunt says there will be an investigation into whether sex pest scandal behaviour has broken ministerial code

Other MPs claimed they had overheard colleagues making light of allegations that had been made while walking to the evening’s debate.

Sir Kevin Barron MP complained that the ability of the Committee on Standards, which he chairs, to tackle sexual misconduct had been clipped by the political parties. He told MPs that in March 2012 the committee, which takes on complaints about MPs’ behaviour, tried to give the commissioner that acts as the final arbiter more scope to investigate.

But he explained: “An amendment tabled by the three major parties’ parliamentary shop stewards, and supported by the frontbenches, was introduced to block this and therefore the Commission was left unable to look into these very important issues.”

European Parliament members protest against sexual harassment

It also emerged that later on, in 2014, senior Tory MPs blocked moves to give commons researchers and secretaries extra protection from sexual harassment.

The 1922 Committee of backbenchers mobilised against an attempt made by David Cameron to create a binding code of conduct that would have included a right for staff members to seek arbitration, amid fears it could lead to politically motivated complaints.

It came as a Cabinet Office investigation got under way into alleged misconduct by International Trade Minister Mr Garnier, with his position looking less than secure after Ms May's official spokesman declined to confirm the Prime Minister has full confidence in him.

The Wyre Forest MP has insisted incidents in which he asked his secretary to buy sex toys and referred to her in sexually inappropriate language, did not amount to harassment, but were merely “high jinks”.

Under Secretary of State for International Trade Mark Garnier has admitted making his secretary buy sex toys and calling her 'sugar t**s' (PA)

While the list of Tory MPs accused of misbehaviour was being circulated in Westminster, Labour members admitted that the problem was something that affected all parties.

Parliamentary authorities met on Monday evening to discuss calls from Ms May for action to tackle bad behaviour, with Mr Bercow backing change amid what he described as “disturbing” allegations of a “culture of sexual harassment”.

But he insisted that in the first instance it was for political parties to “live up to their responsibilities”, given that parliamentary staffers are employed by MPs rather than the Commons authorities.

Setting out details of her plan in the Chamber, with the Prime Minister by her side, Ms Leadsom said the recent spate of allegations against MPs showed current arrangements were “inadequate” and action was needed in “days rather than weeks”.

She stated that behaviour should be deemed inappropriate even if significantly below criminal activity. “If people are made to feel uncomfortable, that is not correct,” she told MPs in the debate called by ex-Labour frontbencher Harriet Harman. “In terms of the consequences for the perpetrators, I think I've also been perfectly clear that in the case of staff they could forfeit their jobs, in the case of Members of Parliament they could have the whip withdrawn and they could be fired from ministerial office.”

Among Ms Leadsom's proposals are a new, more substantial independent helpline service to deal with complaints of sexual harassment and abuse at Westminster. There is also a proposed support team linked to the helpline, that should be able to recommend the onward referral of a case to ensure “appropriate investigation and action”, including being able to “strongly recommend” any criminal allegations are reported to the police.