Counter-terrorism officers have arrested a 50-year-old man at Heathrow Airport as he disembarked a plane from the Egyptian capital Cairo.
The man was arrested under Section 58 of the Terrorism Act 2000 on suspicion of "possession of articles containing information of a kind likely to be useful to a person committing or preparing an act of terrorism".
Scotland Yard said: "The arrest was pre-planned and not in response to any immediate danger but as part of an ongoing investigation into allegations of terrorist activities overseas.
"This arrest is not related to Isis or Syria."
As part of the investigation officers are searching a residential address in north London.
The arrested man is in police custody.