A woman has been arrested on suspicion of conspiring to commit female genital mutilation.
The 38-year-old was arrested at Heathrow Airport as she arrived on a flight from Sierra Leone.
A 13-year-old Sierra-Leonian girl travelling with the woman was taken into the care of social services.
The woman, a British national born in Sierra Leone, remains in custody in a west London police station.
The arrest was made following a week-long initiative at Heathrow Airport aimed at preventing and detecting FGM.