The point that was being made on Radio 4 this morning is that if a 12 or 13 year old girl is acting provocatively, you should be looking at what in her history or, indeed, mental capacity, has led her to behave like that. She may have a history of abuse, or parents or guardians who haven't given her good advice in life, or even a medical condition which is causing her to act inappropriately. You can't just assume that just because she appears to want sex, she has the capacity to consent to it.
Someone else said that in British law there is a line drawn in the sand at 16 years. Both boys and girls below that age are deemed to be incapable of consenting to sex, whatever their individual mental and physical development. As a father of 2 girls (and 1 boy), all of whom are well above that age group thankfully, I am very happy that is the case.
When I was under 16 I was certainly capable of consenting to sex, and would have done if presented with the opportunity. I'm sure we've all known underage boys and girls who have had sex because they wanted to, and not because of some traumatic past. The fact is kids naturally have these desires long before they are deemed old enough to act on them by law. It's ridiculous to try and pretend that's not the case.