Boris Johnson is facing a backlash over the promotion of his ally Chris Pincher, as a group of Conservative parliamentary staffers accused the prime minister of a “failure to act on warnings” of sexual misconduct by his MPs. As new claims emerged about Pincher, who resigned as deputy chief whip over allegations that he groped two men in a London club, No 10 continued to insist that Johnson was unaware of any “specific” warnings until last week. But a whips’ office source acknowledged on Sunday that a “matter” relating to Pincher had in fact been reported to them during the February reshuffle. The source had previously denied receiving any complaints or warnings – formal or informal – about his conduct. Johnson is likely to face questions in parliament this week about what he knew about allegations concerning Pincher, after five further reports of alleged misconduct emerged over the weekend, including groping Tory MPs. Pincher denies all the allegations against him. The warning to the whips’ office in February is believed to have come from a Conservative MP who was the subject of an unwanted pass from Pincher. A second MP told the Guardian they had raised allegations of sexual misconduct by Pincher with their whip, but without making a formal complaint because they were not personally a victim. He said he had told the whips office in February that Pincher should not be in the job because he could not be trusted with young male staff. “I told a whip what I thought of Pincher, and that he had a terrible reputation with younger staff and MPs which had not gone away. That still stands.” The MP said they had not made a specific allegation, because that would have resulted in a full-blown inquiry and he could not guarantee that accusers would come forward. “I would not have wanted to have done that without a victim’s express permission. But I wanted them to know that there were claims out there.” A third MP said they had warned senior figures in the party that “Pincher should not be anywhere near the whips office,” let alone in the deputy role that conferred responsibility for welfare of MPs as well as discipline. There were also reports that Steve Barclay, Johnson’s chief of staff, tried to block Pincher’s appointment and asked for an investigation by the Cabinet Office’s propriety and ethics team. A group of parliamentary aides, called Conservative Staffers for Change, who previously wrote to Johnson with their general concerns about sexual misconduct in Westminster, said on Sunday that the stories now coming out about Pincher “come as no surprise”. “His behaviour was an open secret in Westminster and it is disappointing that this was not addressed sooner,” they said. “Having raised concerns about sexual misconduct with the chief whip, we were disappointed not only by how long it took to remove the whip from Pincher, but also at the continued lack of clarity about the PM’s knowledge of his behaviour. “We wrote the letter to the PM raising concerns about illegal sexual misconduct [by those in power abusing their positions] in May, yet received no response. This is about more than just the culture in Westminster, it is about the PM’s failure to act on warnings of serious misconduct from those in government.” The two parliamentary staffers representing the group are due to meet Lindsay Hoyle, the Speaker, this week to “raise our concerns about parliament as a workplace and how our employment structures can be reformed”. Conservative MPs have also been raising their concerns with their whips about why the party refused to take any allegations about Pincher seriously without a formal complaint by an alleged victim to the Independent Complaints and Grievance Scheme. Anne Milton, the former Conservative deputy chief whip, told the Guardian: “I feel very angry that in this day and age this sort of behaviour still goes on … Victims will come forward if they trust the process and the individual that they are going to. That person doesn’t have to be in the whips office, just a senior person with responsibility. And absolutely witnesses should be able to come forward with complaints. It’s nonsense having a system without that.” Senior Conservatives remain adamant that Tory MP Craig Whittaker stepped down as a whip in February because of outstanding allegations of harassment against Pincher, despite Whittaker’s denial. Whittaker, the MP for Calder Valley, issued a statement to the Halifax Courier on Sunday saying he had stood down as a whip for health reasons, and not because he opposed the appointment of Pincher, as was claimed on Saturday. But one senior Tory source said: “There is no doubt that Craig was concerned about Pincher taking up a key role that gave him power over younger MPs, he has told people that that was the reason. “Are we really supposed to believe that this was not then passed on to the PM? It is stretching the bounds of credibility.” Another younger Tory colleague said: “There were persistent rumours about Chris and how he behaves when drunk, but there are persistent rumours about most people in parliament and if you believed all of them we would have no MPs. “So I was wary of him but I did not fully believe those rumours because I hadn’t come across anyone who said they had actually seen him groping anyone or been groped. Now of course I am saying to myself, ‘should I have said something before?’. But the reality is that it takes a complaint for other complaints to come tumbling out.” On Sunday night, Labour wrote to Johnson demanding answers about how Pincher came to be appointed as the deputy chief whip. In a letter to the prime minister, Anneliese Dodds, the Labour party chair, him asked why he was not asking the party to investigate Pincher, unlike the inquiry into Neil Parish, the Tory MP who resigned for watching pornography in the House of Commons. “Only Boris Johnson could have looked at this guy’s record and thought ‘he deserves a promotion,’” Dodds said. “Not only that, but by not investigating these allegations and allowing the former deputy chief whip to keep the Conservative whip, the prime minister is sending a dangerous signal. “This prime minister is clearly happy to sweep sexual misconduct under the carpet in order to save his own skin. Conservative MPs need to take a long hard look in the mirror and decide if this is the kind of leader the British people deserve.” Pincher has had the whip suspended but Johnson initially held out against this step until a formal complaint about him was made by a victim to the Independent Complaints and Grievance Scheme.