Police are investigating an alleged rape in Parliament.
A 23-year-old man was arrested on suspicion of rape following the alleged attack in the early hours of Friday, the Metropolitan Police said.
Police stressed that the man who had been arrested was not an MP.
A Metropolitan Police spokesman said: "Detectives from the sexual offences, exploitation and child abuse command are investigating an allegation of rape at the Houses of Parliament in the early hours of Friday, 14 October.
"A 23-year-old man was arrested that same day on suspicion of rape. He has been bailed pending further inquires to a date in mid-January 2017."
A House of Commons spokesman said: "We are aware of an incident on the parliamentary estate which is being investigated by the Metropolitan Police Service.
"Parliament is working closely with the police on their investigation and we cannot comment further while this is ongoing."