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.
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"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.