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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Lord Montagu, who founded the National Motor Museum at Beaulieu, has died aged 88 following a short illness.
Expensive fares and late arrivals make Britain's railways "second rate" compared to European rivals, a study has found.
Former England rugby captain Will Carling has played down his country's hopes of success at the 2015 World Cup.