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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ITV News spent the day at the Royal Berkshire Hospital in Reading looking at the lengths it is going to prepare for the winter ahead.
Endris Mohammed must serve a minimum of 33 years after killing his two children with a petrol-soaked cloth before trying to kill his wife.
Three people who had been arrested on suspicion of murder have been released without any further action.