Two addresses in north west and north London
are now being searched
Two women aged 26 and 27 have been arrested on suspicion of terrorism offences, the Metropolitan Police says.
The first was arrested at around 09.20 GMT a as she tried to board a flight to Istanbul in Turkey from Terminal 5.
She was seized on suspicion of being involved in the commission, preparation and instigation of acts of terrorism. A "large quantity" of money was seized.
A second woman, aged 27, was held on suspicion of the same offence in north-west London and taken into custody.
Both women are now being questioned.
Scotland Yard said the arrests were intelligence-led rather than in response to an immediate threat or risk.
Two addresses in north and north-west London are now being searched.