According to the Independent, a report by MPs lays the blame for the lack of prosecutions at the door of political correctness, and I think they’re right.
http://www.independent.co.uk/news/uk/politics/political-correctness-resulting-in-female-circumcision-being-ignored-in-uk-say-mps-8656224.html
It has been said that this is a ‘cultural’ practice, but it should be acknowledged that the ‘culture’ in question is, in the main, Islamic. To deny that in the cause of ‘respect’ for religion – or culture - serves only to disguise the problem – and to exacerbate it. The Koran actually forbids any alteration to Allah’s creation, but since circumcision for both men and women is recommended by the Prophet Mohammed, who is deemed beyond criticism, this horrendous practice is not only acceptable in many communities – it is obligatory.
Education is clearly the answer, but educating mindsets that are firmly entrenched in a grossly backward philosophy is no easy task, and certainly a lengthy one, so short of having all girls under the age of about 16 undergo a quick and simple medical examination once a year, I see no immediate answer.