According to UK media reports, the arrested man is believed to be Sam Armstrong, who is a political aide to Conservative party MP Craig Mackinlay.
"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 Scotland Yard spokesperson said.
"A 23-year-old man was arrested that same day on suspicion of rape. He has been bailed pending further enquires to a date in mid-January 2017," the spokesperson said.
The House of Commons Serjeant at Arms office, which oversees parliamentary security, said that it was aware of the allegation.
"We are working closely with the Metropolitan Police on the matter but cannot comment further at this time," a spokesperson said.
The accused is believed to have taken a woman to Mackinlay's office after he and other Tory party aides got drunk at a bar within the Palaces of Westminster, which houses Britain's House of Commons and House of Lords, late into the night.
According to'The Sun' newspaper, the parliamentary office of Mackinlay, which is in the Norman Shaw North complex, was raided by six officers last week and sealed as a potential crime scene.
Sources told the newspaper the MP was in his constituency at the time of the alleged attack.
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