Boris Johnson’s party has been engulfed in fresh scandal as it emerged a Conservative MP had been arrested on Monday on suspicion of serious sexual offences, including rape. The unnamed man’s arrest on Monday followed a two-year investigation, Metropolitan police said – and related to offences alleged to have been committed between 2002 and 2009. In a statement, the Met said “a man, aged in his 50s, was arrested on suspicion of indecent assault, sexual assault, rape, abuse of position of trust and misconduct in public office. He remains in custody”. “The offences are alleged to have occurred in London. An investigation is ongoing, led by officers from Central Specialist Crime.” Westminster sources suggested some of the offences are believed to have taken place in parliament. The MP’s arrest came as a date was announced for two byelections triggered by the resignation of Conservative MPs. Imran Ahmad Khan, the former MP for Wakefield, was convicted of sexually assaulting a 15-year-old boy; while former Tiverton MP Neil Parish admitted watching pornography in the House of Commons chamber. Both contests will take place on 23 June, with Labour hoping to win in Wakefield, and the Liberal Democrats positioning themselves as the challengers in Tiverton. The LibDems pulled off a shock victory in North Shropshire last year, after Owen Paterson resigned over paid lobbying. Another Conservative MP, David Warburton, who represents Somerton and Frome, has had the whip suspended while under investigation for sexual harassment by the House of Commons’ Independent Complaints and Grievance Scheme. A Conservative Whips’ Office spokesperson said the MP would be asked not to come to parliament. “The chief whip has asked that the MP concerned does not attend the parliamentary estate while an investigation is ongoing. Until the conclusion of the investigation we will not be commenting further.” It is understood no decision will be made about whether to remove the whip from the MP until the police investigation is completed, in order to protect the anonymity of the victims. This latest case will reopen concerns about the culture at Westminster, and whether it is a safe place to work. Garry Graham, deputy general secretary of Prospect union, said: “What will it take for parliament to finally take its responsibility to its staff and visitors seriously and suspend access to the estate for parliamentarians under investigation for sexual offences? “Voluntary agreements to stay away do not work, as demonstrated by Imran Ahmad Khan’s attendance at Westminster whilst investigations were ongoing, despite agreeing to stay away. Parliament has the same responsibilities towards its staff as any other workplace and it must live up to them.” Female Conservative MPs recently met the chief whip to air their concerns about the behaviour of some colleagues – a gathering that led to Parish’s resignation, after his behaviour was discussed. The leader of the House of Commons, Mark Spencer, said last week that his party was committed to selecting higher quality candidates at the next general election, claiming the snap contests of 2017 and 2019 had led to mistakes. “I think we’ll be in a much better place at the next general election, certainly in the [Conservative] party as we will have taken much more time to scrutinise people. There will be a much longer process,” he said. Details of the MP’s arrest emerged during what the government had hoped would be “crime week”, with announcements on toughening up policing. The prime minister told his cabinet on Tuesday morning: “Crime, crime, crime is what we want to focus on.” The Met continues to investigate gatherings held in Downing Street and Whitehall during Covid lockdowns. More than 100 fixed-penalty notices have so far been issued, though Johnson has only been fined once, along with his wife, Carrie Johnson, and the chancellor, Rishi Sunak, for a birthday party held in 2020. Many Conservative backbenchers are concerned about the impact on the Tories’ reputation as the party of law and order – but have so far declined to move against the prime minister by demanding a vote of no confidence.