Peter Mandelson will face a criminal investigation into allegations that he leaked market sensitive information from Downing Street to Jeffrey Epstein, the Press Association (PA) understands.
It comes after emails appeared to show conversations between the pair about government and political matters while Lord Mandelson was serving as business secretary and the de-facto deputy prime in Gordon Brown's government.
Documents released by the US Department of Justice indicate Epstein was sent internal discussions from the heart of the UK government after the global financial crisis.
A number of opposition parties had called for a formal police inquiry.
Downing Street earlier said the Cabinet Office had referred how Mandelson handled sensitive government information while he was a minister to the Metropolitan Police.
Former prime minister Brown said earlier today that he had also written to the force's commissioner, Mark Rowley, about Mandelson's contact with Epstein.
Mandelson has previously said: "I was wrong to believe Epstein following his conviction [in 2008 for procuring a child for prostitution and of soliciting a prostitute] and to continue my association with him afterwards. I apologise unequivocally for doing so to the women and girls who suffered."
In an interview with The Times carried out last week but published on Monday, Mandelson referred to a "handful of misguided historical emails, which I deeply regret sending", and described Epstein as "muck that you can't get off your shoe".