A 26-year-old man has been arrested in east London under the Terrorism Act.
A spokesman for Scotland Yard said counter terror police detained the man at around 5.20pm on Wednesday in a pre-planned operation.
He remained in custody at a south London police station on Thursday.
He has been arrested on suspicion of being involved in the commission, preparation and instigation of acts of terrorism, under section 41 of the Terrorism Act 2000.
A search at a property in east London continues, the force added.
In a statement, the Metropolitan Police said: "Detectives from the Met Police Counter Terrorism Command have arrested a 26-year-old man on suspicion of being involved in the commission, preparation and instigation of acts of terrorism, under section 41 of the Terrorism Act 2000.
"The man was arrested on Wednesday, October 31, in east London at approximately 5.20pm in a pre-planned operation.
"He was taken to a south London police station, where he currently remains in police custody.
"Detectives also executed a search warrant at an address in east London which remains ongoing at this time.
"Enquiries continue."
