A Muslim woman police officer refused to shake hands with the head of the Metropolitan Police on faith grounds.
Sir Ian Blair questioned the validity of the refusal
The officer, who has not been named, was granted the exemption at a passing-out ceremony where new recruits met Commissioner Sir Ian Blair.
The woman's refusal was based on her view that her faith prevented her touching a man other than her husband or a close relative.
Sir Ian had questioned the validity of her refusal, Scotland Yard said.
A spokeswoman for the force said: "This request was only granted by members of training staff out of a desire to minimise any disruption to others' enjoyment and to ensure the smooth running of what is one of the most important events in an officer's career."
She added: "The officer maintains that she puts the requirements of being a police officer above her personal beliefs and only exercises the latter when she has choice to do so.
"Any refusal to engage in this manner would not be tolerated by the MPS (Metropolitan Police Service)."
The woman was allowed to pass out in December last year because she had completed all the elements of the 18-week recruit training course.
This included officer safety training, which required officers to come into physical contact with each other.
The officer will now be required to complete a two-year probationary period.
Muslim groups defended the police officer, saying her beliefs would not affect how she carried out her job and called for greater understanding of different cultures.
Massoud Shadjareh, chairman of the London-based Islamic Human Rights Commission, said: "I don't think shaking hands is something that makes or breaks a relationship.
"I don't think in any sort of job that is something that becomes an obstacle to one performing one's duties."
'Not set in concrete'
Sheikh Ibraham Mogra, of the Muslim Council of Britain, said people should not be alarmed by the officer's beliefs and that Muslim law "was not set in concrete".
He added: "If the officer is called to a male victim who has been shot, the laws go out of the window.
"If she has to resuscitate that dying person, Muslim law will then change and allow her all sorts of physical contact because a life is at risk and life is so precious.
"Muslim law will say, 'forget everything, save this life'."