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."
Head of the Met Police's Sexual Offences, Exploitation and Child Abuse Command said female genital mutilation (FGM) "will not be tolerated in the United Kingdom".
Detective Chief Superintendent Keith Niven said:
Police launched an operation this week at airports across the UK targeting flights to and from countries known to carry out female genital mutilation (FGM).
The joint-force Operation Limelight includes officers at Heathrow Airport speaking with passengers on 13 outbound flights to "high risk" countries.
Passengers were warned that FGM is illegal in the UK and if caught, offenders face a large fine and a prison sentence of up to 14 years.
Flights to Heathrow from Nigeria and Sierra Leone were also targeted as officers sought to identify children subjected to FGM and anyone who may have arranged the procedure.
Mandatory medical examinations to identify victims of female genital mutilation (FGM) may have to be considered in the UK, the Metropolitan Police chief has said.
Sir Bernard Hogan-Howe said there have been a lack of referrals from schools and medical professionals about girls who had undergone the procedure, as an operation was launched at airports to identify possible victims.
An estimated 66,000 women in the UK have undergone FGM and more than 20,000 girls under 15 are thought to be at risk of the practice, which is classed as torture by the UN.
The first UK prosecution for alleged FGM began earlier this year, while there have reportedly been 100 FGM-related convictions in France.
Mayor Boris Johnson told ITV London that the law now needs to be able to expose people performing FGM.
Alimatu Dimonekene told ITV London about her FGM ordeal at the age of 16.