“This follows search warrants at two addresses in the Wiltshire and Camden areas.”
The force is probing claims that the senior British politician leaked internal government discussions to convicted sex offender Jeffrey Epstein in the wake of the 2008 financial crash.
Emails released as part of the Epstein files in the United States appeared to show the then-business secretary forwarding on correspondence to Epstein, triggering fresh scrutiny of his relationship with the late, disgraced financier.
He has not been charged with an offense. Under British law, police can hold a suspect for up to 24 hours before either applying for more time for questioning, charging that person with a crime or releasing them.
Mandelson is one of the architects of New Labour who helped bring Tony Blair to power in 1997. He returned to high office last year when he was named as the British ambassador to Washington despite his known links to Epstein.
He was forced out of that role in September after it was reported he had continued a closer relationship with Epstein after the late financier’s conviction than was previously publicly known.
Mandelson has not commented on the police investigation, but has previously said he was wrong to have continued his association with Epstein and apologized “unequivocally” to Epstein’s victims.