The surgeon who will conduct the operation on the girl, who lives in Cheshire, said the operation was not a purely cosmetic one and was to restore asymmetry to an underdeveloped breast that had been causing her much distress.
"One breast has not developed. On one side she has an A cup and on the other a D cup. She has a problem that she is very upset about," said Douglas McGeorge, who works for both the public and private sector. "She won't go out. She won't go into changing rooms at school. She won't do sport. She won't undress in front of friends.
Because the girl is so young, the implants used will consist of two chambers, one inside the other. The inner chamber is expandable so salt water can be injected through a button on the side of the breast or extracted to alter the size "to balance her out". The outer chamber is silicone to give a more natural feel and appearance.
Mr McGeorge defended the operation yesterday, saying it was more than just a straightforward cosmetic one because of the girl's "psychological and physical needs". He added: "She has an underdeveloped breast. This will allow her to lead a normal life.
"This is surgery for an abnormality which caused enormous distress to the child.Cosmetic surgery for breast enhancement is not something I carry out with children."
Mr McGeorge said he performed around six such operations on girls under 18 each year. The girls are referred to him by GPs. If he felt it was suitable, the operation could go ahead, although sometimes a clinical psychologist would be involved in the process.