The Metropolitan Police chief said a campaign launched to identify possible victims of female genital mutilation (FGM) "warns" people of the law.
Sir Bernard Hogan-Howe said: "They have an option to stop - the fact they bought a ticket to me is irrelevant.
"They should not be committing a serious attack on a child and they should not be breaking the law."
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A woman has been arrested at Heathrow Airport on suspicion of a terrorism offence after arriving on a flight from Turkey.
Social workers across England have blown the whistle on a "threadbare" care system.
The world is facing a "global health emergency", according to the World Health Organisation (WHO).