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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Muhammad Rodwan, 56, who launched a ferocious machete attack on Pc Stuart Outten, has been found guilty of wounding with intent.
A member of her staff said the monarch is "not feeling up to it", so will not attend an event being addressed by broadcaster Huw Edwards.
'Holidays: Bagging a Bargain Break' is on ITV tonight at 7:30pm.