culture change is needed at Westminster, Foreign Secretary Liz Truss said as a Tory MP was bailed pending further inquiries into allegations of rape and sexual assault offences.
Scotland Yard said the unnamed man in his 50s was also detained on suspicion of indecent assault, abuse of position of trust and misconduct in public office.
Ms Truss, who is also Minister for Women and Equalities, said more needed to be done to “professionalise” the way the House of Commons works “but that does not excuse crimes being committed”.
Tory chief whip Chris Heaton-Harris urged the MP to stay away from Parliament but has not suspended the whip, meaning the suspect remains a member of the parliamentary party.
Commons Speaker Sir Lindsay Hoyle confirmed the suspect had agreed to stay away from Westminster and urged fellow MPs not to reveal his identity.
The Metropolitan Police said: “In January 2020, the Met received a report relating to alleged sexual offences having been committed between 2002 and 2009.
“The offences are alleged to have occurred in London.
“An investigation is ongoing, led by officers from central specialist crime.
“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 was taken into custody and has since been bailed pending further inquiries to a date in mid-June.”
It was understood the Conservatives will not make a decision on whether the suspect has the whip suspended until after the police investigation is concluded.
Ms Truss said she was “very, very concerned” that a Tory colleague had been arrested.
She told Sky News: “The police are currently working on the case but it is worrying that we are seeing these appalling … accusations, again, about a parliamentarian.”
Asked if the MP should have been suspended or had the whip withdrawn, she said: “I think it’s a matter for the police about whether that individual is named.
“I don’t know who it is.
“I know that the police are looking at it and investigating it and I think we need to wait for the police to conduct those investigations.”
She told LBC: “I certainly think that the culture of the House of Commons has changed and needs to change further.
“I think there needs to be more to be done to professionalise the way the House of Commons works.
“I would agree with that.
“But I don’t think we can attribute that… I don’t think that’s an excuse for people to commit appalling crimes.”
At the start of Wednesday’s Commons proceedings, Sir Lindsay told MPs: “The House will know that a Member has been arrested in connection with an investigation into an allegation of very serious criminal offences.
“I understand that the member has confirmed he will not attend the House of Commons while the investigation is ongoing.”
Sir Lindsay said the House authorities took the “safety of our staff and parliamentary community as a whole very seriously and are ensuring any necessary measures are taken in respect of MPs, employees and staff”.
The Prospect union, which represents hundreds of staff working in the Houses of Parliament, said firmer action is needed.
Deputy general secretary Garry Graham 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?”
The arrest comes amid renewed scrutiny of sleaze in Westminster following a string of cases.
Former Conservative MP Imran Ahmad Khan quit the Commons earlier this month after being convicted of sexually assaulting a boy.
David Warburton had the Conservative whip withdrawn after allegations of sexual harassment and cocaine use emerged.
Over the past year, around 15 MPs are suspected to have been investigated by Parliament’s Independent Complaints and Grievance Scheme (ICGS) watchdog that examines allegations of bullying, harassment or sexual misconduct.
Neil Parish stood down as the Conservative MP for Tiverton and Honiton earlier this month after admitting watching pornography in the Commons.
The latest arrest also follows a Conservative MP being arrested on suspicion of rape in 2020.
He was never identified and police took no further action after an investigation.
Conservative sources declined to identify the individual in the latest case, citing the need to protect the identity of any complainant.
A statement from the Tory whips’ office said: “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.”