The former Rochdale MP Simon Danczuk has been accused of raping a woman at a property in Westminster.
The politician, who quit the Labour party earlier this week, is alleged to have carried out the attack a year ago.
A Met Police spokesman said: "On Monday, 8 May 2017, officers from Greater Manchester Police (GMP) referred an allegation of rape to the Metropolitan Police.
"A woman has alleged that she was raped by a man in his 50s. The incident is alleged to have occurred in May 2016 at a location in Westminster.
"Detectives from the Sexual Offences, Exploitation and Child Abuse Command have been notified and will investigate. No arrests have been made and enquires continue."
Father-of-four Danczuk, 50, dismissed the allegations levelled against him and said it would not deter him from plans to stand as an MP in the 8 June general election.
"The Metropolitan Police have not been in touch with me about this," he told The Sun.
"It is a totally false allegation and I look forward to the police clearing it up. But I am very intrigued by the timing of it, two days before the closure of nominations for the parliamentary election in Rochdale."
The allegations were reported the same day Danczuk quit Labour after party chiefs banned him from standing as their candidate in the general election over a sexting scandal involving a 17-year-old girl.
Danczuk, who had been suspended since December 2015 over the scandal, plans to try and hold on to his Rochdale seat, which he won from the Liberal Democrats in 2010, as an independent. He will take on Labour candidate Tony Lloyd.
In his resignation letter on Monday, Danczuk said Labour is "no longer the political movement" he joined 30 years ago and that it had "totally lost touch" with its social democratic values.
His exit from the party came as his estranged wife, "selfie queen" Karen, failed in her bid to be selected as a Labour candidate for Bury North in Greater Manchester.
Danczuk has been linked to a string of women since the pair separated in 2015. He is currently engaged to mother-of-two Charlene Meade, 31, who is almost 20 years his junior.