The age of criminal responsibility in UK is 10. You said that you were blackmailed, ask the police why they are not prosecuting the offender?
https://www.gov.uk/age-of-criminal-responsibility
I am also surprised that a girl in under ware is regarded as indecent. Apparently, it is up to a jury to decide. "
Whilst members of a jury are representative of the public, it remains essential for them to consider the issue of indecency by reference to an objective test, rather than applying their wholly subjective views of the matter (R v Neal [2011] EWCA Crim 461)."