Sam Armstrong, chief of staff to South Thanet MP Craig Mackinlay, was arrested last week after accusations that he raped a woman in Parliament.
The 23-year-old has been released on bail while inquiries continue into the incident, which is alleged to have occurred in the early hours of Friday.
According to The Sun, the allegation was made after a group of Tory aides had been drinking on the House of Lords terrace, overlooking the River Thames. Armstrong reportedly took the woman to the MP's Parliamentary office and she reported the alleged attack soon afterwards.
A spokesman for the MP said: "On Friday morning, Mr Mackinlay was made aware of an allegation against a member of his staff.
"Following a request made by the police and parliamentary services he granted full access to his Westminster office. Mr Mackinlay is currently awaiting further information from the police."
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."