Peter Mandelson has been released on bail hours after being arrested on suspicion of misconduct in public office.
Mandelson, 72, has been accused of passing on information to paedophile financier Jeffrey Epstein when he was business secretary.
He was seen being led out of his London home by plain-clothed police officers yesterday evening after a unit searched his home in Wiltshire.
The police said earlier today that a man, 72, had been released pending further investigation.
Mandelson, a former Labour minister and US ambassador, was seen returning to his Camden home by a black cab at around 2am.
The arrest came weeks after police carried out another search in his Camden home with Lord Mandelson present earlier this month.
Deputy Assistant Commissioner Hayley Sewart, previously said: ‘I can confirm that officers from the Met’s Central Specialist Crime team are in the process of carrying out search warrants at two addresses, one in the Wiltshire area, and another in the Camden area.
‘The searches are related to an ongoing investigation into misconduct in public office offences, involving a 72-year-old man.’
Lord Mandelson was pictured in the Epstein files released by the Department of Justice, showing him in his underwear in the financier’s Paris home.
A series of payments has also been found from Epstein to Mandelson and his husband, Reinaldo Avila da Silva.
Lord Mandelson has not responded to the latest allegations, but in an interview with the Times he admitted to a ‘lapse in judgment’ over funding sent by Epstein to his husband Reinaldo for an osteopathy course.
Sir Keir Starmer has said his once-ally Peter Mandelson ‘betrayed our country, our Parliament and my party’.
Starmer admitted knowing about Lord Mandelson’s ongoing friendship with convicted paedophile Jeffry Epstein when he brought him back to government.
The Prime Minister said: ‘He lied repeatedly to my team when asked about his relationship with Epstein before and during his tenure as ambassador, I regret appointing him. If I knew then what I know now, he would never have been anywhere near Government.’

A linchpin of the New Labour project from its birth in the early 1990s, Lord Mandelson witnessed and participated in the feuds that dominated much of its 13 years in power.
His ability to manipulate the levers of power from the shadows earned him monikers such as ‘the Prince of Darkness’ and ‘the Dark Lord’.
A vocal critic of Jeremy Corbyn’s leadership of the Labour Party, Lord Mandelson then provided advice to Sir Keir as he sought to win power.