London police are not naming the man but confirm that the 72-year-old arrested on Monday evening has been released.
Mandelson had close contacts with convicted sex offender Jeffrey Epstein and is suspected of similar crimes to the former Prince Andrew Mountbatten-Windsor.
Mandelson was previously forced to resign from his post as Britain's ambassador to Washington, D.C., after it emerged that his contacts with Epstein were more extensive than he had previously said.
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